Initial commit

LICENSE

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README.md

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+# Macintosh SE Hardware
+
+This is my effort to assemble all the pertinent hardware design
+information on the Macintosh SE into a single coherent information
+repository.  The goal is to be able to have sufficiently detailed
+information to, in theory, reproduce an identical (or nearly so)
+physical, functional copy of the Macintosh SE.
+
+However, my primary interest in having this information available is
+to have detailed information for studying the Macintosh SE hardware,
+and for maintaining existing Macintosh SE computers.
+
+Conventional Macintosh emulator software prioritizes access to
+application software without regard to the mechanical and electrical
+design of the actual machine itself.  My hope is that this repository
+of information will enable the same kind of virtual access to the
+hardware as we have to the vintage Macintosh software through the use
+of conventional Macintosh emulators.
+
+## What is currently available?
+
+Currently, this repository only contains a vector graphics hand
+trace-over of page 1 of the Macintosh SE Main Logic Board (MLB)
+schematics.  Typed text is used for all legible text.  Since pages 2
+and 3 of the MLB schematics are missing and nowhere to be found on the
+Internet, they will have to be redrawn from the reverse engineered
+printed circuit board layout.
+
+Follow this link to [jump to the redrawn
+schematic](old_artifacts/schems/retrace_se_mlb_p1.pdf).
+
+There are lots of other independent projects with good pieces of
+information out and about on the Macintosh SE.  For the time being,
+these are linked from documentation in the repository.  In the event
+the project has a potentially insecure future or lacks a durable
+storage location, the pertinent information is copied into this
+repository.
+
+## See also
+
+Check out the GitHub repository repository with redrawn schematics for
+the Macintosh SE/30:
+
+https://github.com/mishimasensei/macse30mlb
+
+## License
+
+Since a primary goal of this project is to assemble historic
+information into a coherent repository, as much as possible, new
+developments are released into the public domain.  After all, as is
+well understood in the vintage computing community, all patents and
+copyrights are destined to eventually expire with the passing of
+enough time, at which point the covered works cede into the public
+domain.
+
+Therefore, if you don't have an interest in exercising any exclusive
+rights covered under copyright, you might as well simply declare your
+works to enter the public domain early, rather than using a permissive
+license or a copyleft license.  For example, the CERN Open Hardware
+Licence.
+
+In the event that your jurisdiction does not have the concept of the
+public domain, the Creative Commons Public Domain Dedication License
+(CC0) is used as a fallback permissive license.

RECAPPING.md

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+# Recap project links and info
+
+Here is a list of links to various Macintosh SE recapping projects.
+
+----------
+
+https://recapamac.com.au/macintosh-se/

VIDEO.md

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+# Macintosh SE Internal CRT Replacement
+
+Got a Macintosh SE with a non-functional CRT?  No worries, there is
+actually an easy workaround to get video on your Macintosh SE!
+
+The CRT is controlled by 3 digital output signals:
+
+* `VIDOUT`
+* `*HSYNC`
+* `*VSYNC`
+
+These are all 5 V logic signals.  Therefore, they can be packed up
+into a DB-9 connector for TTL or ECL video.  Commercially available
+flat panel displays are avaiable with adapter electronics that can
+accept TTL or ECL video, since it apparently became very popular in
+specialized industrial equipment.  Once you've got your monitor and
+connectors all set up, you should be good to go.
+
+* Visited 2020-08-06:
+  https://allpinouts.org/pinouts/connectors/computer_video/ecl-video/
+* Visited 2020-08-06:
+  https://allpinouts.org/pinouts/connectors/computer_video/monochrome-ttl/
+
+It might be relevant that ECL stands for "Emitter Coupled Logic" in
+other contexts, here is a source for reference.
+
+* Visited 2020-08-06:
+  https://technobyte.org/logic-families-ttl-cmos-ecl-bicmos-difference/

firmware/README.md

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+# firmware
+
+This directory contains firmware images required for the various ROM
+chips in the hardware design.

firmware/adb/README.md

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+# adb
+
+This directory contains the firmware for the ADB (Apple Desktop Bus)
+chip, which is actually an Apple-branded PIC16CR54 microcontroller.

firmware/rom/README.md

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+# rom
+
+This directory can contain ROM dumps of the Macintosh SE's main system
+firmware boot ROM that is directly accessible to the CPU.  However,
+due to their uncertain copyright status, they are currently not
+included in the repository.
+
+Additionally, links to other projects to provide a modern replacement
+ROM for the Macintosh SE are also provided here.

firmware/rtc/MacPlusRTC.cpp

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+#include <avr/wdt.h>
+#include <avr/interrupt.h>
+#include <EEPROM.h>
+
+/****************************************
+ *                                      *
+ * A drop-in replacement for the custom *
+ * RTC chip in early Apple Macintosh    *
+ * computers, using an ATtiny85.        *
+ * Uses an external 32.768kHz crystal   *
+ * on pins 2 and 3 as a clock source.   *
+ *            __  __                    *
+ *     1SEC -|1 \/ 8|- VCC              *
+ *    XTAL2 -|2    7|- RTC.CLK          *
+ *    XTAL1 -|3    6|- RTC.DATA         *
+ *      GND -|4____5|- !RTC             *
+ *                                      *
+ ****************************************/
+
+const int      ONE_SEC_PIN = 1;   // A 1Hz square wave on PB5
+const int  RTC_ENABLE_PIN =  5;   // Active low chip enable on PB0
+const int  SERIAL_DATA_PIN = 6;   // Bi-directional serial data line on PB1
+const int SERIAL_CLOCK_PIN = 7;   // Serial clock input on PB2
+
+const int PRAM_SIZE = 256;        // Mac Plus used the xPRAM chip with 256 bytes, time is a separate 4 additional bytes
+//const int PRAM_SIZE = 20;         // Models earlier than the Plus had 20 bytes of PRAM
+
+volatile byte serialBitNum = 0;
+volatile byte address = 0;
+volatile byte serialData = 0;
+
+
+enum SerialStateType { SERIAL_DISABLED, RECEIVING_COMMAND, SENDING_DATA, RECEIVING_DATA };
+volatile SerialStateType serialState = SERIAL_DISABLED;
+
+volatile unsigned long seconds = 0;
+volatile byte pram[PRAM_SIZE] = {}; // 256 Bytes of PRAM, the first four of which count the number of seconds since 1/1/1904
+
+/*
+ * The following is potential locations of various bits of PRAM data, none of this is in any way certain:
+ *    Sound volume is in pram[0x08]
+ *    Alert sound is in param[0x7c - 0x7d]
+ *    Machine location and timezone is in pram[0xE4 - 0xEF]
+ */
+
+
+/*
+ * An interrupt to both increment the seconds counter and generate the square wave
+ */
+void halfSecondInterrupt() {
+  PINB = 1<<PINB0;  // Flip the one-second pin
+  if(!(PINB & (1<<PINB0))) { // If the one-second pin is low
+    seconds++;
+  }
+}
+
+/*
+ * The actual serial communication can be done in the main loop, this way the clock still gets incremented
+ */
+void handleRTCEnableInterrupt() {
+  serialBitNum = 0;
+  address = 0;
+  serialData = 0;
+  if(!(PINB&(1<<RTC_ENABLE_PIN))){ // Simulates a falling interrupt
+    serialState = RECEIVING_COMMAND;
+//    enableRTC = true;
+  } else {                         // Simulates a rising interrupt
+    clearState();
+  }
+}
+
+void clearState() {
+    DDRB &= ~(1<<DDB1);   // Return the pin to input mode
+    PORTB |= (1<<PORTB1); // Set pullup resistor
+    serialState = SERIAL_DISABLED;
+    serialBitNum = 0;
+    address = 0;
+    serialData = 0;
+}
+
+/*
+ * The ATtiny has EEPROM, lets use it to store the contents of PRAM in case of power failure, 
+ * this is an improvement over the original, still a good idea to keep the chip powered by a 
+ * battery or supercapacitor so that the clock continues to advance.
+ * 
+ */
+void savePRAM() {
+  noInterrupts(); // Don't update the seconds counter while we're saving it to ROM, probably unnecessary
+  for(int i = 0; i < 4; i++) {
+    EEPROM.update(i,(seconds>>(8*i))&0xff);
+  }
+  interrupts(); // Go ahead and interrupt us while we save the rest
+  for(int i = 0; i < PRAM_SIZE; i++) {
+    EEPROM.update(i+4,pram[i]);
+  }
+}
+
+
+void goToSleep() {
+  bitClear(MCUCR,SM0);  // The two SM bits must be set to 00 to enter idle mode
+  bitClear(MCUCR,SM1);  // Sleeping in other modes will disable the timer
+  bitSet(MCUCR,SE);
+  __asm__("sleep" "\n\t");
+  bitClear(MCUCR,SE);
+}
+
+void setup() {
+  noInterrupts(); // Disable interrupts while we set things up
+  
+  pinMode(ONE_SEC_PIN, OUTPUT);             // The 1Hz square wave (used, I think, for interrupts elsewhere in the system)
+  pinMode(RTC_ENABLE_PIN, INPUT_PULLUP);    // The processor pulls this pin low when it wants access
+  pinMode(SERIAL_CLOCK_PIN, INPUT_PULLUP);  // The serial clock is driven by the processor
+  pinMode(SERIAL_DATA_PIN, INPUT_PULLUP);   // We'll need to switch this to output when sending data
+  
+  wdt_disable();      // Disable watchdog
+  bitSet(ACSR,ACD);   // Disable Analog Comparator, don't need it, saves power
+  bitSet(PRR,PRTIM1); // Disable Timer 1, only using Timer 0, Timer 1 uses around ten times as much current
+  bitSet(PRR,PRUSI);  // Disable Universal Serial Interface, using Apple's RTC serial interface on pins 6 and 7
+  bitSet(PRR,PRADC);  // Disable Analog/Digital Converter
+
+  bitSet(GIMSK,PCIE);   // Pin Change Interrupt Enable
+  bitSet(PCMSK,PCINT0); // turn on RTC enable interrupt
+
+//  for(int i = 0; i < 4; i++) {
+//    seconds += ((unsigned long)EEPROM.read(i))<<(8*i);
+//  }
+//  for(int i = 0; i < PRAM_SIZE; i--) { // Preload PRAM with saved values
+//    pram[i] = EEPROM.read(i+4);
+//  }
+  
+  //set up timer
+  bitSet(GTCCR,TSM);    // Turns off timers while we set it up
+  bitSet(TIMSK,TOIE0);  // Set Timer/Counter0 Overflow Interrupt Enable
+  TCCR0B = 0b111;       // Set prescaler, 32,768Hz/64 = 512Hz, fills up the 8-bit counter (256) once every half second
+  TCNT0 = 0;            // Clear the counter
+  bitClear(GTCCR,TSM);  // Turns timers back on
+  
+  interrupts(); //We're done setting up, enable those interrupts again
+}
+
+void loop() {
+  if(digitalRead(RTC_ENABLE_PIN)) {
+    clearState();
+    goToSleep(); 
+  } else if(digitalRead(SERIAL_CLOCK_PIN)) {
+    switch(serialState) {
+      
+      case RECEIVING_COMMAND:
+        bitWrite(address,7-serialBitNum,digitalRead(SERIAL_DATA_PIN));
+        serialBitNum++;
+        if(serialBitNum > 7) {
+          boolean writeRequest = address&(1<<7);  // the MSB determines if it's a write request or not
+          address &= ~(1<<7); // Discard the first bit, it's not part of the address
+          serialBitNum = 0;
+          if(writeRequest) { 
+            serialState = RECEIVING_DATA;
+            serialBitNum = 0;
+          } else {
+            if (address < 4) {
+              serialData = (seconds>>(8*address))&0xff;
+            } if(!(address&0b0110000)) { // Apparently this address range is off-limits for reading
+              serialData = pram[address];
+            }
+            serialState = SENDING_DATA;
+            serialBitNum = 0;
+            pinMode(SERIAL_DATA_PIN, OUTPUT); // Set the pin to output mode
+          }
+        }
+        break;
+        
+      case RECEIVING_DATA:
+        bitWrite(serialData,7-serialBitNum,digitalRead(SERIAL_DATA_PIN));
+        serialBitNum++;
+        if(serialBitNum > 7) {
+          if(address < 4) {
+            noInterrupts(); // Don't update the seconds counter while we're updating it, bad stuff could happen
+            seconds = (seconds & ~(((long)0xff)<<address)) | (((long)serialData)<<address);
+            interrupts();
+          } else {
+            pram[address] = serialData;
+          }
+//          savePRAM();
+          clearState();
+        }
+        break;
+        
+      case SENDING_DATA:
+        digitalWrite(SERIAL_DATA_PIN,bitRead(serialData,7-serialBitNum));
+        serialBitNum++;
+        if(serialBitNum > 7) {
+          clearState();
+        }
+    }
+  }
+}
+
+/*
+ * Actually attach the interrupt functions
+ */
+ISR(PCINT0_vect) {
+    handleRTCEnableInterrupt();
+}
+
+ISR(TIMER0_OVF) {
+    halfSecondInterrupt();
+}

firmware/rtc/README.md

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+# RTC
+
+This directory contains a work-in-progress firmware for implementing a
+drop-in replacement for the RTC on ATTiny85 microcontroller.  I've
+made a few modification to this particular copy, but it still needs
+more work to be fully functional.
+
+Source, Visited 2020-08-05:
+
+* https://www.reddit.com/r/VintageApple/comments/91e5cf/couldnt_find_a_replacement_for_the_rtcpram_chip/e2xqq60/
+* https://pastebin.com/baPZ4nN4

hardware/3d_print/README.md

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+# 3d_prints
+
+This directory contains 3D printable parts like the external enclosure
+case, etc.

hardware/README.md

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+# hardware
+
+This directory contains design files, schematics, and related
+documentation for hardware components.

hardware/fpga/README.md

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+# fpga
+
+This directory contains hardware description language (Verilog/VHDL)
+source files for the Field Programmable Gate Arrays (FPGAs) that
+implement the functions of the custom Application Specific Integrated
+Circuits (ASICs) found in the original hardware.

hardware/fpga/bbu/README.md

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+# "BBU" Apple Custom Silicon
+
+The "BBU", as it is called on the Macintosh SE's printed circuit board
+silkscreen, is a relatively complex Apple custom silicon chip,
+compared to the other custom chips on the Macintosh SE's Main Logic
+Board (MLB).  Despite its intimidating look as a chip with a huge
+number of pins, its purpose can be summarized as follows.
+
+* Provide a single address bus interface to ROM, RAM, and I/O devices,
+  including simple digital I/O pins.
+
+* Scan the CRT by driving the primary digital control signals
+  (`*VSYNC`, `*HSYNC`, `VIDOUT`).
+
+There might be additional processing functions it may provide as a
+convenience between the CPU and the various other hardware chips, but
+chances are these processing functions are relatively simple.
+
+Most of the I/O pins that are connected to the BBU are single-bit
+digital I/O signals that are relatively easy to understand.  Reverse
+engineering the Macintosh SE's firmware may be required to determine
+how these pins are mapped into the CPU's address space, but once that
+determination is made, providing a replica interface to most of the
+connected hardware should be super-easy.
+
+The following I/O chips are connected to the BBU:
+
+* VIA interrupt controller
+
+* IWM/SWIM floppy disk controller
+
+* SCSI Controller
+
+* Serial Communications Controller (SCC)
+
+Other chips that are connected to the BBU are mainly interfaced via
+only simple, single-pin interfaces.

hardware/fpga/bbu/bbu_pinout.csv

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+BBU Pin,Signal Name,Description,Device Connection,Device Pin
+1,GND,,,
+2,RD7,,,
+3,RD8,,,
+4,RD9,,,
+5,RD10,,,
+6,RD11,,,
+7,RD12,,,
+8,RD13,,,
+9,RD14,,,
+10,RD15,,,
+11,EXTPDS,,,
+12,EN245,Select Data Buffer,74LS245,
+13,VCC,,,
+14,/WR,,,
+15,/CAS-SIMM3,,SIMM3,2
+16,/CAS-SIMM1,,SIMM1,2
+17,/EOP,,53C80,
+18,/CAS-SIMM4,,SIMM4,2
+19,/CAS-SIMM2,,SIMM2,2
+20,/RAS,,,
+21,GND,,,
+22,VCC,,,
+23,A23,,,
+24,A22,,,
+25,A21,,,
+26,A20,,,
+27,A19,,,
+28,A17,,,
+29,A9,,,
+30,/IPL1,,68000,
+31,/IPL0,,68000,
+32,IRQ,,65C22/6523,
+33,/LDS,,68000,
+34,/BERR,,68000,
+35,/UDS,,,
+36,/VPA,,68000,
+37,CK,,68000,
+38,/DTACK,,68000,
+39,SELROM,Select ROM,ROM,"20 on ROM HI, LO"
+40,"RTxCB, PCLK, ADB CLK",All the things,"85C30, ADB, GLU","20 & 28 on 85C30, 16 on ADB, 9 on GLU"
+41,/AS,,,
+42,VCC,,,
+43,GND,,,
+44,FCLK,,"SWIM, GLU","24 on SWIM, 19 on GLU"
+45,SELSCC,Select SCC,85C30,32 on /CE
+46,/RD,,85C30,
+47,R/W,,,
+48,SELSWIM,Select SWIM,SWIM,7 on /DEV
+49,EXTFLP,PWM,External Floppy,10 on PWM
+50,PB7,,65C22/6523,
+51,SELSND,Select Sound,SND,
+52,EXTPDS,,,
+53,PA6,,65C22/6523,
+54,/LDS,,,
+55,DRQ,,53C80,22 on DRQ
+56,/DACK,,53C80,26 on /DACK
+57,SELSCSI,Select SCSI,53C80,21 on /CS
+58,SELVIA,Select VIA,65C22/6523,24 on RS0
+59,/RST,,,
+60,HSYNC,Horizontal Sync,J12,Pin 10 on J12
+61,VSYNC,Veritcal Sync,"J12, 65C22/6523","Pin 11 on J12, 40 on DB7"
+62,VIDOUT,Composite Video Out,"J12, 65C22/6523","Pin 9 on J12, 28 on PC3"
+63,GND,,,
+64,VCC,,,
+65,RA9,,,
+66,RA7,,,
+67,RA8,,,
+68,RA6,,,
+69,RD0,,,
+70,RA5,,,
+71,RA4,,,
+72,RD1,,,
+73,RA3,,,
+74,RD2,,,
+75,RD3,,,
+76,RA2,,,
+77,RD4,,,
+78,RA1,,,
+79,RA0,,,
+80,RD5,,,
+81,/PMCYC,,74F257,/OE
+82,EN257,Select Address Buffer,74F257,
+83,RD6,,,
+84,VCC,,,

hardware/fpga/glu/README.md

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+# GLU
+
+The GLU chip is a Programmable Array Logic (PAL) chip used to
+facilitate I/O logic and the like.  In particular, it is a PAL16L8.
+The equation list and fusemap that can be used to program a modern
+ATF16V8 chip is contained here.

hardware/fpga/rtc/README.md

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+# RTC Apple Custom Silicon
+
+The RTC (Real-Time Clock) chip within the Macintosh SE is an Apple
+custom silicon chip that implements the real-time clock and
+battery-backed PRAM (Parameter RAM).  Fortunately, its simplicity has
+yielded a fairly complete replacement chip design that is based around
+the pin-compatible ATTiny85 chip running appropriate firmware.  See
+the `firmware` directory for details.
+
+Nevertheless, if we do get a microscopic chip scan of the original
+silicon, this directory would contain corresponding design files to
+replicate the original design as-is.  Since the chip design is so
+simple, this might be easily doable with conventional DSLR macro
+photography after the packaging is opened up.

hardware/pcb/README.md

@@ -0,0 +1,3 @@
+# pcb
+
+This directory contains Printed Circuit Board (PCB) designs.

hardware/pcb/mlb/README.md

@@ -0,0 +1,13 @@
+# mlb
+
+This directory contains the schematics and circuit board design for
+the Macintosh SE Main Logic Board (MLB).
+
+PDF schematics, Gerber files, and other generated files are found in
+the [output](output) directory.
+
+Check out this forum thread on the 68kMLA where development on reverse
+engineering and replicating the Macintosh SE's MLB is happening.
+
+https://68kmla.org/forums/index.php?app=forums&module=forums&controller=topic&id=60059
+

hardware/pcb/mlb/output/README.md

@@ -0,0 +1,4 @@
+# Generated Artifacts
+
+This directory contains files/data that have been generated from
+source files within.

old_artifacts/README.md

@@ -0,0 +1,12 @@
+# old_artifacts
+
+This directory contains pertinent information that came from the
+original manufactured and distributed artifacts.
+
+* [schems](schems): Scans and vector retraces of photocopied
+  schematics distributed to anyone who requested them.
+
+* [mlb_stock_photos](mlb_stock_photos): Photographs of the
+  mass-production manufactured Macintosh SE main logic board, as is
+  typically photographed for the sake of Internet forum communications
+  and sales, as opposed to reproduction-oriented photos.

old_artifacts/mlb_stock_photos/.gitignore

@@ -0,0 +1,2 @@
+recapamac_se_mlb.jpg
+wikipedia_se_mlb.jpg

old_artifacts/mlb_stock_photos/README.md

@@ -0,0 +1,11 @@
+These are links to helpful photos of the of the Macintosh SE Main
+Logic Board (MLB).
+
+PLEASE NOTE: The MLB in the photo from `recapamac.com` is hacked.
+
+Source URLs of accompanying web pages and photos:
+
+* Visited 2020-08-05: https://en.wikipedia.org/wiki/Macintosh_SE
+* Visited 2020-08-05: https://upload.wikimedia.org/wikipedia/commons/6/65/Apple_Macintosh_SE_Main_PCB.jpg
+* Visited 2020-08-05: https://recapamac.com.au/macintosh-se/
+* Visited 2020-08-05: https://recapamac.com.au/wp-content/uploads/2019/08/mac_se_logic.jpg

old_artifacts/mlb_stock_photos/get_photos.sh

@@ -0,0 +1,8 @@
+#! /bin/sh
+# Use a shell script to download the photos so that we do not add
+# bloat to the repository size that we don't strictly need.  GitHub
+# has bandwidth limits, so let's try to keep away from those as much
+# as possible.
+
+curl -L https://upload.wikimedia.org/wikipedia/commons/6/65/Apple_Macintosh_SE_Main_PCB.jpg -o wikipedia_se_mlb.jpg
+curl -L https://recapamac.com.au/wp-content/uploads/2019/08/mac_se_logic.jpg -o recapamac_se_mlb.jpg

old_artifacts/schems/.gitignore

@@ -0,0 +1,3 @@
+se_mlb_p1.gif
+se_mlb_p1_tmp.png
+se_mlb_p1_proc.png

old_artifacts/schems/Makefile

@@ -0,0 +1,17 @@
+all: retrace_se_mlb_p1.pdf
+
+se_mlb_p1.gif: 
+	./get_scans.sh
+
+se_mlb_p1_proc.png: se_mlb_p1.gif
+	./resize-mlb-scan.sh
+
+retrace_se_mlb_p1.pdf: retrace_se_mlb_p1.svg se_mlb_p1_proc.png
+	inkscape --export-pdf=$@ $<
+
+mostlyclean:
+	rm -f se_mlb_p1_tmp.png
+	rm -f se_mlb_p1_proc.png
+
+clean: mostlyclean
+	rm -f se_mlb_p1.gif

old_artifacts/schems/README.md

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+These are links to the official Apple Macintosh SE schematics.
+
+Source website: https://museo.freaknet.org/gallery/apple/stuff/mac/andreas.kann/schemat.html
+
+Unfortunately, there are no BOMARC schematics available for the
+Macintosh SE.
+
+The Internet Archive also has a copy of purportedly the same Macintosh
+SE schematics scan.
+
+https://archive.org/details/Macintosh68kSchematics
+
+----------
+
+Due to the illegiblity of the original Main Logic Board (MLB) page 1
+scan, this repository also contains a retrace of the schematic,
+striving to be as faithful as possible to the original.  The retrace
+was done by hand and careful eyeing in Inkscape, after doing some
+simple image processing on the input scan.  A script that uses the
+ImageMagick `convert` command is included to reproduce the processing
+steps.
+
+Notes related to the accuracy of the retrace.
+
+* The pinouts of all integrated circuit components have been verified
+  with second sources.
+
+* The pinouts of the PDS slot and RAM SIMMs have **not** yet been
+  verified with second sources.
+
+* The resistor values have been checked to be consistent with the
+  reference designators, but **not all reference designators** have
+  been verified to be consistent with the placement on the printed
+  circuit board.
+
+* The schematic info blocks in the upper and lower left corners have
+  been cross-checked with scans of other official Apple schematics to
+  attempt to make them as faithful as possible to the original
+  contents.
+
+Notes on the source SVG file:
+
+* The processed scan is linked as a hidden and locked image object.
+  To view both the retrace and the original scan together, find the
+  image object (possibly in the XML hierarchy) and make it visible.
+  The image object is locked to make it easier to draw on top of.
+
+* The specific `sans-serif` font I used on my system is DejaVu Sans.
+  So long as your system `sans-serif` font has similar metrics,
+  everything should work just fine, otherwise you can replace the font
+  family name with DejaVu Sans.

old_artifacts/schems/get_scans.sh

@@ -0,0 +1,7 @@
+#! /bin/sh
+# Use a shell script to download the scans so that we do not add bloat
+# to the repository size that we don't strictly need.  GitHub has
+# bandwidth limits, so let's try to keep away from those as much as
+# possible.
+
+curl -L -o 'se_mlb_p1.gif' https://museo.freaknet.org/gallery/apple/stuff/mac/andreas.kann/SE_P1.GIF

old_artifacts/schems/resize-mlb-scan.sh

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+#! /bin/sh
+# Given the input illegible scan of the Macintosh SE Main Logic Board
+# Page 1 schematic, apply some image processing magic on it to make it
+# somewhat more legible.
+
+# Here's how our image processing operations work.
+#
+# 1. The original scanned image is monochrome.  Gradation is expressed
+#    linearly through the means of error-diffusion half-toning.
+#
+# 2. To convert to grayscale, we simply convert to 8-bit grayscale and
+#    then resize to 80%, using a cubic resize image filtering
+#    algorithm.  The resulting 8-bit intensity values will be
+#    expressed in a linear sample space.  We then resize by 250% to
+#    get a grayscale image, linear intensity samples, that is twice
+#    the spatial resolution of the original.
+#
+#    The second resizing step is mainly to ease looking at zoomed in
+#    copies of the image, which you must do almost all the time due to
+#    the illegibility of the original.
+#
+# 3. If the image is displayed directly on sRGB displays, it will
+#    appear artificially dark because it is currently using linear
+#    intensity samples, but an sRGB display uses a curve
+#    (approximately gamma = 2.2) to map the image samples to linear
+#    light intensities.  Just leave it this way because the source
+#    image is already pretty light to begin with.  The artificial
+#    darkening makes the image easier to read.
+#
+#    To get a gamma-correct image, we would need to apply a `gamma =
+#    0.45` curve to the image.  Or, in other words, "gamma-correct" by
+#    a factor of `1/0.45 = 2.2`.  Alternatively, we could use the more
+#    precise sRGB colorspace conversion function.
+
+set -e # Exit on errors.
+
+# N.B. We use two conversion command lines because I think otherwise
+# ImageMagick just replaces the previous resize command with the new
+# resize command and would only end up resizing the image once.
+
+convert -depth 8 -resize 80% -filter cubic se_mlb_p1.gif se_mlb_p1_tmp.png
+convert -resize 250% -filter cubic se_mlb_p1_tmp.png se_mlb_p1_proc.png
+rm se_mlb_p1_tmp.png