AM186ES Advanced Micro Devices, AM186ES Datasheet - Page 76

• Manufacturer Part Number: AM186ES
• Description: microcontrollers provide a low-cost/ high-performance solution for embedded system designers who wish to use the x86 architecture.
• Manufacturer: Advanced Micro Devices

5.5.2
Figure 5-2
Table 5-3
5-6
Low Memory Chip Select Register
(LMCS, Offset A2h)
The Am186ES and Am188ES microcontrollers provide the LCS chip select pin for the
bottom of memory. Since 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.
Before activating the LCS chip select, the width of the data bus for LCS space should be
configured in the AUXCON register.
The Low Memory Chip Select is configured through the LMCS register (see Figure 5-2).
Low Memory Chip Select Register
The value of the LMCS register at reset is undefined except DA is set to 0.
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 Am186ES and
Am188ES microcontrollers.
The Am186ES and Am188ES microcontrollers have a block size of 512 Kbytes, which is
not available on the 80C186 and 80C188 microcontrollers. Table 5-3 outlines the possible
configurations.
LMCS Block Size Programming Values
Memory Block
128K
256K
512K
Size
64K
Address
15
A19
0FFFFh
1FFFFh
3FFFFh
7FFFFh
Ending
0
UB2–UB0
Chip Select Unit
1 1 1
UB2–UB0
000b
001b
011b
111b
1
DA
7
PSE
1 1 1
R2
R1–R0
0