Force Computers SYS68K/CPU-40, User Manual

Page: 18 / 372

SECTION 1 INTRODUCTION
2-5
2.2.3 The SRM-01/4
The SRM-01/4 is a 4 Mbyte RAM module which is used on the CPU-41B/4.
Features of the SRM-01/4
!
4 Mbyte SRAM
!
Burst READ and Burst WRITE capability
!
Battery Backup via VMEbus
!
Accessible via VMEbus
The access address for the 68040 is $00000000 to $003FFFFF.
The access address for the VMEbus is programmable in 4 Kbyte steps through the FGA-002. The defined
memory range can be write protected in coordination with the address modifier codes. For example, in
supervisor mode the memory can be read and written, in user mode memory can only be read.
Parity check is not necessary for SRAM devices, because these components are protected against soft
errors owing alpha emission. The following chart lists the required CPU clock cycles and wait states for
accessing the shared RAM.
Board 68040 Clock No. of CPU Clock No. of CPU Clock No. of Wait No. of Wait
Type Frequency Cycles Counted Cycles for States for States for
From TS to TA Burst Cycles Normal Cycles Burst Cycles
for Normal Cycles
CPU-41/B 25 MHz 3 1 2 0