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M80C186
15
1
14
M6
13
M5
12
M4
11
M3
10
M2
9
8
7
6
5
1
4
1
3
1
2
1
0
OFFSET:
A8H
M1
M0
EX
MS
R2
R1
R0
Figure 13. MPCS Register
15
U
A19
9
U
3
1
0
OFFSET:
A6H
U
U
U
U
U
1
1
1
1
1
R2
R1
R0
A13
Figure 14. MMCS Register
MMCS bits R2–R0 specify READY mode of opera-
tion for all mid-range chip selects. All devices in mid-
range memory must use the same number of WAIT
states.
The 512K block size for the mid-range memory chip
selects is a special case. When using 512K, the
base address would have to be at either locations
00000H or 80000H. If it were to be programmed at
00000H when the LCS line was programmed, there
would be an internal conflict between the LCS ready
generation logic and the MCS ready generation log-
ic. Likewise, if the base address were programmed
at 80000H, there would be a conflict with the UCS
ready generation logic. Since the LCS chip-select
line does not become active until programmed, while
the UCS line is active at reset, the memory base can
be set only at 00000H. If this base address is select-
ed, however, the LCS range must not be pro-
grammed.
Peripheral Chip Selects
The M80C186 can generate chip selects for up to
seven peripheral devices. These chip selects are ac-
tive for seven contiguous blocks of 128 bytes above
a programmable base address. This base address
may be located in either memory or I/O space.
Seven CS lines called PCS0–6 are generated by the
M80C186. The base address is user-programmable;
however it can only be a multiple of 1K bytes, i.e.,
the least significant 10 bits of the starting address
are always 0.
PCS5 and PCS6 can also be programmed to provide
latched address bits A1, A2. If so programmed, they
cannot be used as peripheral selects. These outputs
can be connected directly to the A0, A1 pins used
for selecting internal registers of 8-bit peripheral
chips. This scheme simplifies the hardware interface
because the 8-bit registers of peripherals are simply
treated as 16-bit registers located on even bounda-
ries in I/O space or memory space where only the
lower 8-bits of the register are significant: the upper
8-bits are ‘‘don’t cares.’’
The starting address of the peripheral chip-select
block is defined by the PACS register (see Figure
15). This register is located at offset A4H in the inter-
nal control block. Bits 15–6 of this register corre-
spond to bits 19–10 of the 20-bit Programmable
Base Address (PBA) of the peripheral chip-select
block. Bits 9–0 of the PBA of the peripheral chip-se-
lect block are all zeros. If the chip-select block is
located in I/O space, bits 12–15 must be pro-
grammed zero, since the I/O address is only 16 bits
wide. Table 10 shows the address range of each
peripheral chip select with respect to the PBA con-
tained in PACS register.
15
U
A19
6
U
5
1
3
1
0
OFFSET:
A4H
U
U
U
U
U
U
U
U
1
R2
R1
R0
A10
Figure 15. PACS Register
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