AMD Am186TMER ユーザーズマニュアル
Chip Select Unit
5-6
5.5.2
Low Memory Chip Select Register (LMCS, Offset A2h)
The Am186ER and Am188ER microcontrollers provide the LCS chip select pin for the
bottom of memory. Because the interrupt vector table is located at 00000h at the bottom
of memory, the LCS pin has been provided to facilitate this usage. The LCS pin is not active
on reset, but any write access to the LMCS Register activates this pin.
bottom of memory. Because the interrupt vector table is located at 00000h at the bottom
of memory, the LCS pin has been provided to facilitate this usage. The LCS pin is not active
on reset, but any write access to the LMCS Register activates this pin.
The Low Memory Chip Select is configured through the LMCS Register (see Figure 5-2).
Figure 5-2
Low Memory Chip Select Register (LMCS, offset A2h)
The value of the LMCS Register at reset is undefined.
Bit 15: Reserved—Set to 0.
Bits 14–12: Upper Boundary (UB2–UB0)—The UB2–UB0 bits define the upper boundary
of the memory accessed through the LCS chip select. Because of the timing requirements
of the LCS output and the nonmultiplexed address bus, the number of programmable
memory sizes for the LMCS Register is reduced compared to the 80C186 and 80C188
microcontrollers. Consequently, the number of programmable bits has been reduced from
eight bits in the 80C186 and 80C188 microcontrollers to three bits in the Am186ER and
Am188ER microcontrollers.
of the memory accessed through the LCS chip select. Because of the timing requirements
of the LCS output and the nonmultiplexed address bus, the number of programmable
memory sizes for the LMCS Register is reduced compared to the 80C186 and 80C188
microcontrollers. Consequently, the number of programmable bits has been reduced from
eight bits in the 80C186 and 80C188 microcontrollers to three bits in the Am186ER and
Am188ER microcontrollers.
The Am186ER and Am188ER microcontrollers have a block size of 512 Kbyte, which is
not available on the 80C186 and 80C188 microcontrollers. Table 5-3 outlines the possible
configurations and the differences between the 80C186 and 80C188 microcontrollers and
the Am186ER and Am188ER microcontrollers.
not available on the 80C186 and 80C188 microcontrollers. Table 5-3 outlines the possible
configurations and the differences between the 80C186 and 80C188 microcontrollers and
the Am186ER and Am188ER microcontrollers.
Table 5-3
LMCS Block Size Programming Values
Memory
Block
Size
Ending
Address
UB2–UB0
Comments
64K
0FFFFh
000b
128K
1FFFFh
001b
256K
3FFFFh
011b
512K
7FFFFh
111b
Not available on the 80C186 and 80C188 microcontrollers
1
15
7
0
0
UB2–UB0
1 1 1
PSE
1 1
1
A19
R1–R0
R2
DA