From bb3d40787a59e0bfbc15b77eb32a30677b2ecb83 Mon Sep 17 00:00:00 2001 From: "Joshua M. Thompson" Date: Sat, 3 Apr 2021 02:10:38 -0400 Subject: [PATCH] Updated the README --- README.md | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 102 insertions(+), 3 deletions(-) diff --git a/README.md b/README.md index 075a083..90bec37 100644 --- a/README.md +++ b/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.