Zilog Z80230 - Manual (Page 262)

SCC/ESCC
User Manual
UM010903-0515 Application Notes
255
J19 is factory set according to the size of the SRAMs provided.
For 32K x 8 SRAMs, jumpers are installed between J19-J2 and J19-J3, and between J19-J5 and
J19-J6, with J19-J1 and J19-J4 left open.
For 128K x 8 SRAMs, jumpers are installed between J19-J1 and J19-J2, and between J19-J4 and
J19-J5, with J19-J3 and J19-J6 left open.
32K x 8 SRAMs have cyclic/redundant addressing starting at
40000
,
80000
, and
C0000
. The
only configuration in which this causes problems is with three pairs of 32K x 8 SRAMs and
275122 EPROMs. In this case, there is a conflict in the range
E0000-EFFFF
.
This conflict can be avoided by any of the 
following methods:
• Using two pairs of 32K x 8 SRAMs
• Using one pair of 128K x 8 SRAMs
• Using 27256 EPROMs, or
• Using 27512 EPROMs but programming 
the size of UCS like they are 27256s
Since the LCS output of the 80186 is not used, the LCMS register in the 80186 is not written with
any value.
Programming the Peripheral Chip Selects
The 80186 allows the PCS6-PCS0 pins, which in this case select the various Datacom controllers,
to be asserted for a selected 896-Byte block of addresses. The block may reside in either memory
or I/O space depending on the values programmed into the PACS and MPCS registers, locations
A4H
and
A8H
of the 80186’s Peripheral Control Block, respectively.
The choice of address space depends on the needs of the customer’s application and the configura-
tion of software supplied with the board as listed in Table . The 81 in the MS Byte of the MPCS 
values (see Table ) makes each MCS3-MCS0 pin correspond to a 2 KB block of addresses in 
memory space. The actual active pin addresses are determined by the value written into the
MMCS register, location
A6H
of the 80186 Peripheral Control Block.
One pair of 128K x 8
devices
256 KB at
00000-
3FFFF
Two pair of 128K x 8
devices
512 KB at
00000-
7FFFF
Three pair of 128K x 8
devices
768 KB at
00000-
BFFFF
Standard Memory Populations
One pair of 32K x 8
devices
64 KB at
00000-
0FFFF