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RC2014 Assembly

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1. Introduction

The RC2014 is a classic kit-style homebrew computer nominally designed around a Z80 CPU and Microsoft BASIC or CP/M. This page is intended to document our (mis)adventures with this fascinating device.

2. Troubleshooting Attempts

This section is under construction!

Please stay tuned for updates pending research and development.

Oscilloscope shows clock, address, and data lines are active. Cannot get it to send or receive anything on the SIO/2 serial ports. Tx and Rx just stay high even when sending data from the PC. Rx shows input when power is off but gets pulled high when on...
Attached a logic probe to CE line on serial SIO/2. Output is very non-deterministic between boot attempts (power cycles are indicated by long "low" stretches.) Screenshot of logic analyzer: several longer periods of line high interrupted by longer periods of line low. The periods of line high contain very rapid low-high activity in irregular patterns.
Got a bigger logic analyzer. It seems to be doing a whole string of NOPs but then eventually it starts executing from the ROM. 0xf3 0xc3 0x93 0x01 are the first four bytes at 0x2000 in the ROM dump. There are glitches here and there but that might just be the analyzer... Screenshot of logic analyzer: Z80 decoder is enabled and shows a few NOP instructions before showing instructions indicating CPU is reading from ROM.
Walked each pin in each backplane connector to ensure all lanes are continuous between connectors and there is NO continuity between adjacent pins (except for double 5V pins and double ground pins). Determined lots of noise on serial line when backplane connected to power and turned OFF if either ROM board or clock board are connected. Based on this, built replacement ROM board with no change in behavior (including when powered off with new ROM and no clock inserted).
Success! It seems the issue was failure to connect the "link" pin on the pageable RAM card, possibly combined with a faulty serial terminal adapter masking this during earlier tests (which works with other things, but is very iffy with the RC2014 in particular!) When using the serial terminal adapter that came with the new Pride kit, a prompt is received (although it freezes on loading CP/M):
Press [SPACE] to activate console
Z80 SBC Boot ROM 1.1 by G. Searle
Type ? for options
Boot CP/M?
Loading CP/M...
An extreme closeup of the RC2014 Pro paged RAM card, where the
Assembled enough of the Pride kit so that it can boot, and it boots successfully! The Pro kit also boots successfully when using the CF module v2.1 from the Pride kit. The Pro CF card works in the v2.1 CF module, but nothing works in the v1.3 CF module from the Pro kit. At least the issue is narrowed down, and we can boot into CP/M, now!

Table of Contents

  1. Introduction
  2. Troubleshooting Attempts