S-100 Bus Analyzer Project Summary

User Questions

Question 1: C64 as S-100 Bus Card

Can the Commodore 64 (C64) CPU, RAM, and ROM be remade as an S-100 bus card to use software like Hesmon and BASIC PEEK/POKE to monitor other cards on the S-100 bus?

Question 2: S-100 Bus Analyzer for TDL Xitan

Without original TDL Xitan software, can an S-100 bus system analyzer be created to test the functionality of other cards in the system and verify if they are working correctly?

Final Response Summary

Creating an S-100 bus analyzer for the TDL Xitan is feasible using a Z80-based card inspired by TDL’s ZPU/SMB, leveraging recovered TDL software like the Zapple monitor and TDL BASIC. The analyzer would monitor bus signals, test card functionality (memory, I/O, interrupts), and diagnose issues. Key components include a Z80 CPU, 64KB RAM, 8KB EPROM with Zapple, and buffered bus interfaces with LEDs. Existing resources (e.g., Zapple binaries, TDL archives) and emulators like Z80PACK enable software development. The card uses 74LS245/244 buffers, probes bus lines, and runs diagnostics via Zapple commands (M, O, G) or custom Z80 code. Prototyping with KiCAD and PCBs from JLCPCB costs ~$70-150. Community support is available via S100Computers and VCFED.

Implementation Steps

1. Prototype: Use an S-100 prototype board; wire components.
2. Schematics: Adapt open designs (e.g., S-100 Bus Debug, Bus Display).
3. Fabricate: Design in KiCAD; order PCBs (~$20).
4. Test: Verify standalone, then full bus via extender.
5. Emulate: Test software in Z80PACK first.

Example Diagnostic Code

PEEK:  ; Peek at address in HL
       LD A, L     ; Low byte to A
       OUT (PORT), A ; Output to bus port
       IN A, (PORT)  ; Read back
       ; Display A via serial
       RET
        

Resources

Resource	Description	Link
Zapple Monitor	TDL’s ROM monitor for memory/I/O testing.	Herb Johnson’s TDL Page
TDL BASIC	Scripting for I/O tests.	Maben’s Archive
Z80PACK	Emulator for Z80/TDL software.	Z80PACK
S-100 Community	Support for schematics/parts.	S100Computers Group

Next Steps Offered

• Detailed Z80 diagnostic code.
• KiCAD schematic tweaks.
• Emulation setup guide.

Generated by Grok 3 on October 14, 2025.