Blogs

Quick ref: Pass arguments to machine code from the Monitor

Submitted by S.Elliott on April 28, 2023 - 6:18pm
When calling a machine code subroutine from the Monitor, one or two additional arguments can be passed by taking advantage of the way the Monitor uses delimiters to parse arguments from its command-line and stores them in the zero-page pointers A1, A2, A3, A4...in an arbitrarily-strange order:
  • The default argument is always the subroutine address, stored in A1.
  • Appending a '.' delimiter allows another argument to be stored in A2.
  • Inserting a '<' delimiter allows an argument to be stored in A4.
Tags: 
monitor
asm

Apple Presents...Easter Egg!

Submitted by S.Elliott on April 5, 2023 - 5:40pm
Back in 1983, how many users found the secret message in this instructional software?

]BRUN BARGLE

Bargle program by Sue Espinosa

Bargle Bargle Bargle

]

Tags: 
easter egg

Transmitting a simple datagram via Video Vapor

Submitted by S.Elliott on April 4, 2023 - 5:36pm
Synopsis:
  • Define a short datagram to be transmitted via vapor from visible screen memory.
  • Encode single-cycle accurate video phase via vapor datagram.
  • Construct a routine to receive the vapor datagram and synchronize itself to the video scanner.
  • Write a simple BASIC program to demonstrate all that!
Tags: 
vaporlock
asm

A few tests for a non-booting Disk II controller

Submitted by S.Elliott on April 1, 2023 - 12:23am
A collection of simple (simplistic) tests for diagnosing a non-booting Disk II or A2 disk controller:
  • Monitor commands to test 6 of the 8 data latches in the 9334 chip
  • Monitor commands to load just one sector, then beep and break
  • Attach an LED to troubleshoot individual latches Q0 through Q3
  • Use a flashlight to "candle" circuit traces
  • Use wood or bamboo to scrape debris off the circuit board
Tags: 
troubleshooting

Clumsy (but pretty!) attempts to map video scanner's memory access

Submitted by S.Elliott on March 28, 2023 - 10:30pm
Some experiments and variously messy results from trying to map how often the video scanner reads each byte of screen memory while creating each video frame.

Green indicates bytes that were detected only once per frame.

Purple indicates bytes that were detected twice per frame.

Orange indicates bytes that were detected thrice per frame.

Blue indicates bytes that were detected four times or more per frame.

Tags: 
vaporlock

Upgrade the Disk II controller with shrouded headers

Submitted by S.Elliott on March 21, 2023 - 12:45am
Apple chose bare headers for the disk connectors on the Disk II controller, which make it notoriously easy to connect the drive cable incorrectly.

Jameco's "Shrouded Box Header 20 Pin 2316R-20G" makes an ideal replacement.

Tags: 
hardware

The chaotic shambles of EPROM voltages, from 2708 through 2764

Submitted by S.Elliott on March 15, 2023 - 8:58pm
Early EPROMs required an unruly assortment of positive and negative power supplies, variously different programming voltages, an assortment of programming voltages.  And they adopted inconsistent part numbering schemes to distinguish these features.

Most surprisingly -- and irritatingly -- manufacturers gradually switched to elevated power supply voltages during programming.  So a 1977 Intel 2716 can be programmed with VCC=5 volts, whereas a 1988 AMD 2716 requires VCC=6 volts during programming.  And Texas Instruments's horribly-complicated TM2716 requires VCC=12 volts during programming!

Tags: 
EPROM

Explore an AP-64, with and without firmware

Submitted by S.Elliott on March 8, 2023 - 8:49pm

There are a lot of AP-64 variants around, so let's explore this clone.  Nexo Distribution sold it to me as "APX-EPROM-1" in March 1988.

First, here's a close look at the firmware socket and booster circuit.

Tags: 
EPROM
AP64

Apple fest 1983 40th Anniversary Poster

Submitted by Khaibitgfx on March 8, 2023 - 3:35pm

The following file is standard poster size, and can be printed by whatever print shop nearest you.

 

Pages

Subscribe to Blogs