ZRCC Memory, I/O map

Memory Map

The memory is consists of 128K of RAM in four 32-K banks:

Top 32K of RAM is the common memory. The bottom 32K can be bank selected by writing to bank select register at I/O location 0x1F as follow:

  • 0x0 is normal operation. This is the reset value
  • 0x1 available, no specific assignment
  • 0x2 is for bank 0 of CP/M-3
  • 0x3 is the top 32K of physical memory. This is the common memory that should not map to the lower 32K in normal operation.

I/O Map


A hardware receiver is implemented in CPLD with the following I/O addresses:

  • Read-only serial data receive register at 0xF9
  • Read-only serial receive status register at 0xF8 where
  • D[0] is the receive ready flag, 1 indicates data is ready, 0 indicates no data
  • Write-only bit-bang transmit register at 0xF9
  • The content of D[0] appears on the TX output pin. D[0] is high at reset. Software must “bit-bang” D[0] of transmit register to emulate the serial port transmit function.

Compact Flash Registers

Compact flash registers are 0x10 to 0x17

Bank Select Register

Bank select register is write only located at 0x1F. Reset value of bank select register is 0x0

bit 0 controls RAM address 15

bit 1 controls RAM address 16

bit 3 controls LED and jumper pad T4

bit 4 controls 64 byte ROM page. When low (the reset value), the first 64 bytes of memory, 0x0-0x3F are mapped to CPLD internal ROM. When high, all memory are mapped to RAM. Once bit 4 is set high and internal ROM is disabled, it will remain high until next reset.

builderpages/plasmo/zrcc/zrcc1/mem_map_zrcc1.txt · Last modified: 2020/05/17 13:02 by plasmo
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