Updated the README

README.md

@@ -1,4 +1,103 @@
-ssc
-===
+# Simple Serial Card
 
-The Simple Serial Card is a low-cost Super Serial Card work-a-like.
+## Overview
+
+The Simple Serial Card is a low-cost Super Serial Card work-a-like. I designed
+this because I needed a way to use ADTPro on my Apple IIe, and the price of
+super serial cards on eBay is getting a bit high for my taste.
+
+This card is more or less 100% compatible with the original Apple card. It
+uses the same 6551 ACIA mapped to the same I/O locations, and in fact can
+use the same firmware ROM.  It does however have some minor differences in the
+interest of cost:
+
+1. There are no DIP switches, so you cannot set the default configuration. It
+   does, however, include a jumper that can be removed to disable IRQs.
+2. Instead of a DB-25 it is wired to use a DB-9 cable like those used by PC
+   motherboards.
+3. There is no terminal/modem block to change the serial port wiring. Just use
+   the appropriate cable instead, or a null modem adapter.
+
+The KiCAD schematics and PCB layout are included. It is a four layer board,
+because my fab house of choice charges the same for 2 and 4 layers, so I went
+with what made the layout easier.
+
+## Parts List
+
+* A 74HCT245 octal bus transceiver (U1)
+* A 28C256 EEPROM (U2)
+* A 1.8432 MHz 5V oscillator (U3)
+* A 22V10 GAL (any speed or variety should work) (U4)
+* A W65C51N ACIA (U5)
+* Two MAX3232 RS-232 line transceivers (U6, U7)
+* Seven 0.1uf ceramic bypass caps (C1-C7)
+* Eight 1uf 16V electrolytic caps (C9-C16)
+* A 2x5 pin header (J1)
+* A 1x2 pin header (J2)
+
+## Assembly
+
+Before assembly you will need to burn firmware ROM into the EEPROM, and burn
+the appropriat equations into the GAL. See "Burning the ROM" and "Burning the
+GAL" below for more details.
+
+I would suggest socketing all of the chips, but at the very least socket the
+ROM and the GAL in case you need to update them.
+
+As mentioned above the header on this card is wired the same as a PC COM
+header. There are two varieties of these cables available; this card uses the
+newer style which is wired 1:1; that is, pin 1 on the header goes to pin 1
+on the DB-9, pin 2 to pin 2, etc. These are sometimes referred to as
+"AT/EVEREX" style cables.
+
+There is an asterisk on the card's silkscreen indicating pin one on the RS-232
+header; make sure this lines up with pin one on your ribbon cable. Usually this
+is the red wire on the ribbon cable.
+
+## Installation
+
+Turn off the computer, put the card in an empty slot, and mount the DB-9 on one
+of the small cutouts on the back of the computer (or just run the ribbon cable
+through an open cutout if you don't care).
+
+## Design Considerations
+
+Many parts choices were influenced by what I have already in my parts bin, even
+if that makes the design non-optimal. For example, I used MAX3232 line drivers
+because I have a ton of them. With 12V available on the slots I could've used
+different parts and avoided all the charge pump caps, but I didn't feel like
+buying more chips.
+
+With the exception of the 22V10 GAL used for glue logic all parts in this design
+are still actively available. The GALs are out of production but still readily
+available on eBay or Aliexpress (though YMMV as far as quality).
+
+## Burning the ROM
+
+A standard super serial card image should work fine with this card, though
+since there are no configuration switches the default settings after power on
+or reset will be somewhat random.  Once I have working cards built I will be
+creating a customized firmware ROM that sets the defaults to 9600 bps for the
+ADT Pro bootstrap.
+
+Since 2K EPROMs are nearly impossible to find I subbed in an AT28C256 EEPROM
+(again, I had one already). Only the lower 2K is used by the card, so when
+burning you can either duplicate the image 16 times, or fill the upper 30K
+with zeroes or some other random data. In theory a AT28C64 EEPROM should also
+work (and only waste 6K), but I don't have one to test, and a brief search
+suggests they aren't any cheaper than the AT28C256 (presumably because they
+are out of production).
+
+I use the TL866 II+ USB programmer along with the minipro Linux client for my
+ROM burns.
+
+## Burning the GAL
+
+The equations for the GAL are included as a .pld file for the GALasm program.
+If you run Linux or another OS that can run GNU make then you should be able
+to just type "make" in the "gal" subfolder to compile the equations into a
+.jed file.  Burning this file requires a suitable programmer; I personally
+use the same TL866 II+ that I use for burning ROMs, though at least at the time
+of this writing the minipro client doesn't know how to burn GALs properly, so
+you'll need to use the official client software, either on a Windows PC or
+under Wine.