SC523, v1.0, Description

SC523 is a Z80 programmable ‘ROM’ card designed for Z50Bus.

This card is designed for firmware developers.

It provides the read-only memory for a Z80-based system. In this case, however, the term “read-only” is not really correct as data can be written to it.

The card houses a FLASH chip which contains the boot-up firmware, such as the Small Computer Monitor (SCM). It also houses a “shadow” RAM chip (pseudo-ROM) which is arranged such that writing to the ‘ROM’ area causes the data to be written to the “shadow” RAM.

Once the “shadow” RAM contains the required firmware image, the memory select switch can be used to reconfigure the memory such that reading is from “shadow” RAM, which is now write-protected.

The main features are:

  • 128k bytes FLASH (4 banks of 32k bytes)
  • 128k bytes RAM (shadow ‘ROM’)
  • Status LED
  • Jumper selection of memory bank, or
  • Software control of memory bank
  • Write protect jumper for FLASH memory
  • Compatible with Z80 CPU card SC518 plus memory card SC519
  • Compatible with Z80 processor SC516
  • The card can be disabled by writing to port 0x38

A typical system will also requires:

  • Backplane (eg. SC501, SC508, SC515, or SC522)
  • Power and reset card (eg. SC502)
  • Z80 CPU and memory:
    • Z80 processor card (eg. SC516 with ROM chip removed), or
    • Z80 CPU + Z80 memory (eg. SC518+SC519 with FLASH chip removed)
  • Serial card (eg. SC511, SC520, or SC521)

Homebrew 8-bit retro computing