Search found 488 matches
- 01 Mar 2019, 19:32
- Forum: Hardware and software hacking
- Topic: Expansion bus
- Replies: 98
- Views: 92425
Re: Expansion bus
Here's a new schematic for the evolving concept. Expansion3.png Ken suggested using a 32-pins RAM socket. With this you can put in the original 32K chip, or upgrade with a single 64K or 128K chip. I added a 74'00. Space-wise this is still a win, and finally there is a true 7400 in the design! That c...
- 28 Feb 2019, 08:06
- Forum: Hardware and software hacking
- Topic: Parts values needed, kit build on hold!
- Replies: 1
- Views: 2513
Re: Parts values needed, kit build on hold!
The schematics are linked on the Gigatron website , under "Manuals and references --> Data Sheets". All part values are in there. There are many ways to build one of course. We recommend 1N60P or BAT42 compatible diodes, especially when using 74LS logic. (But don't use 74 LS 04 for the clo...
- 27 Feb 2019, 23:29
- Forum: Hardware and software hacking
- Topic: Expansion bus
- Replies: 98
- Views: 92425
Re: Expansion bus
The glue logic would look like this: /O_SEL = /OE | /WE # Write to I/O /WE_RAM = ~/OE | /WE # Disable RAM write during I/O /I_SEL = /OE | ~SCLK # Read from I/O /OE_RAM = /OE | SCLK # Disconnect RAM from bus during I/O So we need four OR gates and 2 inverters. If we squeeze, this can be done by three...
- 27 Feb 2019, 19:27
- Forum: Hardware and software hacking
- Topic: Expansion bus
- Replies: 98
- Views: 92425
Re: Expansion bus
Blinkenlights on the RAM board have become a must-have in the industry:
https://youtu.be/V5T3_7feo1U?t=32
https://youtu.be/V5T3_7feo1U?t=32
- 26 Feb 2019, 15:08
- Forum: Hardware and software hacking
- Topic: Expansion bus
- Replies: 98
- Views: 92425
Re: Expansion bus
Indeed, I believe that will work. The SPI mode is restricted, but that's fine. Or we just use more flip-flops and untangle the RAM /CE from SCK. Software-wise, our video/sound loop has no free cycles during the horizontal pulse (let alone three of them). But we could try to transfer 8 bits in one SY...
- 24 Feb 2019, 20:48
- Forum: Hardware and software hacking
- Topic: Expansion bus
- Replies: 98
- Views: 92425
Re: Expansion bus
I just realise my previous rambling doesn't really work for the input scenario: /IOSEL comes too late. It must be derived from /W instead: /IOSEL = /OE | /W _ _ _ CLK | |_| |_| |_ ____ ___ /W |___| ____ ___ /OE |___| ____ ___ /IOSEL |___| <-- input through 74'244 to bus(*) ______ ___ /WE |_| <-- bus...
- 24 Feb 2019, 16:32
- Forum: Hardware and software hacking
- Topic: Expansion bus
- Replies: 98
- Views: 92425
Re: Expansion bus
I need to give this a rest for a couple of days. This is hard to let go. Once started, the cogs of the mind continue turning, even when doing other things. So I added glitch suppression to the schematic in the same way as on the main board with the /WE signal: mute the signal during the first phase...
- 22 Feb 2019, 21:10
- Forum: Hardware and software hacking
- Topic: Expansion bus
- Replies: 98
- Views: 92425
Re: Expansion bus
I think visually, so I converted your original proposal to a schematic. I believe it's pretty much a correct transcription, but not 100.0% sure of that. Also PDF and KiCAD files attached. [I spent most time fighting the standard KiCAD component library, as the 74LS30 has its output declared as input...
- 22 Feb 2019, 19:39
- Forum: Hardware and software hacking
- Topic: Maze generation in gigatron assembly
- Replies: 1
- Views: 2223
Re: Maze generation in gigatron assembly
Excellent! Good that we caught the SYS call issue quickly. I caught another thing when uploading this to real hardware: sendFile.py had become unreliable in combination with the Arduino Uno . You can get this message: Connecting to /dev/tty.usbmodem14101 Exception: Gigatron offline A bug had crept i...
- 22 Feb 2019, 18:07
- Forum: Hardware and software hacking
- Topic: Expansion bus
- Replies: 98
- Views: 92425
Re: Expansion bus
I decided to measure it on a standard Gigatron with 32K and ROM v3. Primary probe (yellow) on the A15 breakout. Secondary probe (blue) on CLK1 so we have a frame of reference. During normal operation one expects A15 always to remain low, because the software isn't trying to access non-existing RAM (...