The RIBBBITN3RDing BitPump

The RIBBBITN3RDing BitPump

The RIBBBITN3RDing BitPump r0.1

A little bit of background 

I've been trying quite a few new things with my RIBBBIT65 designs, and I'm running into issues which aren't making a lot of sense.  I've also been having some trouble isolating issues (e.g. "known good" components or circuits don't work *here*... and it turns out "known good" wasn't)  I wanted to have a way that I could repeatably, and quickly, put a bunch of R65 Bus signal configurations ... snapshots, if you will... on the bus to confirm the thing is behaving the way I expect.  Rather than coding something up in 6502 Assembly for every different testing scenario - and, in the process, intoroducing the possibilty that the CORE board I'm using has a problem, I thought it would be better to do something like my TTL Busy Boxes, but on steroids.  The Busy Boxes are just boards with switches and/ or lights that let you do some multiple of 8 worth of switching and/or indicating.  The first one I designed has an 8-position DIP switch, 8 mini-tac switches, and a 10-segment LED bar graph.  That's great for, say, the data bus.  There's still the address bus (16 bits) and all the control signals.  Well, controlling 32 (or more) signals via DIP switches and/or Mini-Tac switches through 20 or 30 cycles (to test an ACIA or a VIA) just seemed like a nightmare.  ...if only there was a way to repeatably send out pre-defined bit patterns over regular time intervals...

The BitPump

The RIBBBITN3RDing BitPump is intended to be an easily reconfigurable digital signal generator which can provide the bit patterns necessary for in-circuit testing of subsystems which interface with 8-bit microcomputers.  

The BitPump, configured for use with the RIBBBIT65 provides:

• an 8-bit bidirectional Data Bus
• a 16-bit output-only Address Bus
• 4 jumpered CPU Control signals (VPB, RWB, MLB, SYNC)
• Jumpered Pull-ups for 5 CPU Control Inputs (SOB,RDY,BE,NMIB,IRWB,RSTB)
• 8 bits of completely manual switching, both latching and momentary on each bit, with indicator LEDs
• 1 "bus clock" driven by a separate IO pin from the bit pattern

The BitPump uses a RaspberryPi Pico (or simlar) to drive a set of four serial-to-parallel shift registers.  

The lower 8 bits (which in the original configuration are wired to the data bus) are bidirectional, and the data direction is controlled by the same "control bit" which drives the R65's RWB (Read, Not-Write) line.  In "Read" mode, the data lines from the bus are displayed on the LEDs.

Since the BitPump is driven by a RaspberryPi Pico (or equivalent), the user has the ability to easily re-program the device to send whatever bit patterns are desired at whatever speed is desired (within the confines of 74HCTXX switching speeds and the capabilities of the sytem under test).

Uses of the BitPump

I'm planning to use the BitPump to see what's going on with my Mini-ITX design.  There's definitely something rotten in Denmark.... hopefully I'll be able to use the BitPump's lower speed, and "known good" bit patterns to isolate the problem(s).  Similar story on the "CORE Daugher Support" board, which is basically supposed to provide a serial console, IO selects, pull-ups and a few other things to the CORE Daughter board I designed for the ITX MoBo, to just make it minimally interactive and runnable.  I plan to troubleshoot both these boards using bit pattern sets delivered by the BitPump.

After that , I plan to use the BitPump to test out different ways of running the 40x4 character LCDs I have.

I can also use it for direct testing of IO and memory chips, since the "data bus" is bidirectional.

What can you use it for?  I dunno.  You could build one and try it out.

Possible updates to the BitPump

One thing I think might be nice is a knob to control the "clock speed".  This could be done easily with a pot and one of the PWM inputs on the Pico.

Another thing that might be nice is a manually controlled "RUN/STOP/STEP" thing that could be done with a couple digital inputs on the Pico.

Do you have any ideas?