Arcom SC88T, Technical Manual

Page: 15 / 34

Section 6. Memory Map
The 80188 CPU has several programmable chip-select lines, which are asserted
when the CPU address falls within the chip-select boundaries defined in the
CPUs internal chip select registers. Upon reset, the 80188 asserts the Upper
Memory-Chip Select (UCS) to select EPROM1 (IC16), and jumps to location
0FFFF0H. The first instructions must be to re-set the Upper Memory Chip Select
register (UMCS) as in the table below, then jump to some code lower in (IC16).
This code can then set up the MMCS and MPCS registers, by which time both
EPROMS will be properly selected. An example of this is given at the end of the
assembly language program in Appendix D.
If EPROM0 (IC14) is not to be used then it will not be enabled if the MMCS
register is left unaccessed. If IC14 is to be used, then using the values in the table
below , EPROM0 will occupy memory directly below IC16, forming a
contiguous block. This also imposes the restriction that EPROM0 and EPROM1
must be the same size.
Because UCS overlaps MCS3, the number of programmable wait states must be
identical for the UCS and MCSO-3 . Two wait-states will be required by slow
EPROMs. If STEbus memory overlaps MCS1 and MCS0 then MCS0-3 must
accept externally generated wait-states until DATACK* is received from the bus
. Both the above conditions are satisfied by the contents of the table below. Slow
EPROMs are those of 250ns access time and above. Note that Arcom use two
wait-states in their initialisation code. This allows the use of any EPROM
currently available.
The RAM is selected by the Lower Memory Chip-Select (LCS), which may be set
from 8k (one 8k RAM) to 64k (two 32k RAMs). Wait-states are not usually
required for fast static RAMs.
If a memory access is made to an address which is within neither UCS, MCS2 or
LCS, the STEbus will be selected automatically. This may result in a bus timeout
if no actual memory exists on the bus. The tables below contain chip select
register values for various RAM and EPROM sizes. EPROM IC16 and IC14 must
be the same size.
Page 15
J90 SC88T 2192-08819-000-000
Total EPROM
capacity
16k
32k
64k
128k
2764 8k
27128 16k
27256 32k
27512 64k
FE3E
FC3E
F83E
F03E
F802
F002
E002
C002
8438
8838
9038
A038
Individual
EPROM type,
size
Register contents (hex)
UMCS MMCS MPCS
Total RAM
8k
16k
32k
64k
6264
6264
55257
55257
----
6264
-----
55257
01F8
03F8
07F8
0FF8
IC15 IC17 LMCS