Teensy 3.2 based Pixie Video Simulator for the 1802 Membership Card
This code simulates a cdp1861 Pixie Video chip, using a Teensy 3.2. This simulator uses a video ram buffer with a 128 x 64 graphics display supported by the U8G2 graphics library as a video display. The code will simulate the interrupts, external flag 1 signal, and DMA Output requests from the original pixie video. This allows programs written for the original Cosmac Elf hardware to run directly on the simulator. This simulator supports 32 x 64 and 64 x 64 video resolutions.
The Teensy 3.2 is available from PJRC. and is also sold by Sparkfun and Adafruit.
U8G2 supports many kinds of 128 x 64 displays. A list of supported displays is available here.
For example, this SSD1306 I2C 128 x64 OLED display available from Adadruit works fine with the Teensy 3.2 and is supported by Uthe 8G2 graphics library.
Here are some examples running actual CDP1802 programs.
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| Close up of SH1106 128x64 OLED display with 1802 Membership card running Cosmac Elf Spaceship program. | Close up of SH1106 128x64 OLED display with 1802 Membership card running Tom Pittman's DMA Test program. |
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| Close up of SH1106 128x64 OLED display with 1802 Membership card running Tom Pittman's Seconds Clock program. | Close up of SH1106 128x64 OLED display with 1802 Membership card running Text Demo program. |
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| Close up of SH1106 128x64 OLED display with 1802 Membership card running Sprite Demo program. | 1802 Membership card, Teensy 3.2, OLED display and wiring. |
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| Close up of Teensy 3.2, 74LS374 Octal D Latch, OLED display and wiring. | |
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| Hardware Schematic | |
- Video Resulton
- Resolutions of 64 x 64 and 32 x 64 are directly supported.
- For 128 x 64 and other resuolutions, video data will be captured on every other DMA request (as per a 64 x 64 resolution).
- Data Lines
- Data lines from the Membership Card ROM at U2 are latched by a 74LS374 Octal D Flip-flip triggered by TPB.
- The latched Data lines are connected to the Teensy 3.2 Port D pins (pins 2, 14, 7, 8, 6, 20, 21, 5)
- The Teensy 3.2 reads data as a byte in a single instruction from Port D during an 1802 DMA Output cycle.
- Full details about Teensy 3.2 pin connections are in the code comments.
- Video Control
- The 1802 Instruction INP 1 (Input from Port 1,1802 Opcode 69) will turn video processing ON.
- The 1802 Instruction OUT 1 (Output to Port 1, 1802 Opcode 61) will turn video processing OFF.
- The /EF1 line will go LOW four lines before a frame's DMA requests begin, and during the last four DMA request lines of a frame.
- An Interrupt Request will be asserted (/INT = LOW) exactly 29 instruction cycles before the first DMA request
- 128 lines of 8 DMA_OUT requests will be asserted per frame. Each DMA_OUT request takes one instruction cycle.
- Exactly 6 instruction cycles will occur between each line of DMA requests.
- There are a minimum of 1882 instruction cycles between frames to simulate the blanking period.
- Software for the 1802 that rely on these control timings will work with this simulator. (If not, please open an issue.)
- Timing details are documented in the code comments.
- Teensy Port 1 Interrupt
- A rising signal on N0 (Port 1) triggers an interrupt on the Teensy 3.2 to turn video on or off.
- Input and Output to Port 1 is used to turn video on or off.
- INP 1, 1802 opcdode 69 (N0 = 1, /MRD = HIGH) turns video on.
- OUT 1, 1802 opcode 61 (N0 = 1, /MRD = LOW) turns video off.
- Teensy TPB Interrupt
- A rising signal on TPB triggers an interrupt on the Teensy 3.2.
- The Teensy interrupt handler will process one cycle in the video state machine
- During DMA the interrupt handler will read the video data byte from Port D (pins 2, 14, 7, 8, 6, 20, 21, 5)
- There are 8 bytes of video data read per frame line.
- Video data is captured every other DMA line and stored in a Video Buffer
- Frame rate and OLED update rate
- After one complete frame of data is captured, the OLED display will be updated.
- Any I2C 64 x 128 OLED supported by U8G2 should work as a display.
- If the captured video data does not change, the display will not be updated for that frame.
- During the display update, interrupts will continue, but data will not be captured for the frame.
- Control signals are maintained during the OLED display updates, so that programs will run correctly, even when data is not captured.
- The 1802 will see frames requests at rate of about 61/second, but the OLED display will actually be updated about 5 times/second.
- /src/MCard1802TeensyPixieVideo/
- MCard1802TeensyPixieVideo.ino -- Teensy 3.2 based Pixie Video simulator for 1802 Membership card and a 128 x 64 graphic display.
- /docs -- documentation files
- MCard1802TeensyPixieVideo.pdf -- schematic for Pixie Video simulation logic using a Teensy 3.2
- Cdp1802SampleProgramCode.txt -- Sample 1802 code listings for various programs.
- /pics -- example pictures for readme
This code is public domain under the MIT License, but please buy me a beer if you use this and we meet someday (Beerware).
References to any products, programs or services do not imply that they will be available in all countries in which their respective owner operates.
Sparkfun, the Sparkfun logo, and other Sparkfun products and services are trademarks of the Sparkfun Electronics Corporation, in the United States, other countries or both.
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Other company, product, or services names may be trademarks or services marks of others.
All libraries used in this code are copyright their respective authors.
Universal 8bit Graphics Library Copyright (c) 2016, olikraus All Rights Reserved
The Teensy 3.2 hardware and software Copyright (c) 2016-2020 by Paul Stoffregen, PJRC.com LLC
The 1802 Membership Card Microcomputer Copyright (c) 2006-2020 by Lee A. Hart.
Many thanks to the original authors for making their designs and code avaialble as open source.
This code, firmware, and software is released under the MIT License.
The MIT License (MIT)
Copyright (c) 2020 by Gaston Williams
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