AM186ES Advanced Micro Devices, AM186ES Datasheet - Page 74

• 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

5.5.1
Figure 5-1
Table 5-2
5-4
Upper Memory Chip Select Register
(UMCS, Offset A0h)
The Am186ES and Am188ES microcontrollers provide the UCS chip select pin for the top
of memory. On reset, the microcontroller begins fetching and executing instructions starting
at memory location FFFF0h, so upper memory is usually used as instruction memory. To
facilitate this usage, UCS defaults to active on reset with a default memory range of 64
Kbytes from F0000h to FFFFFh, with external ready required and three wait states
automatically inserted.
The UCS memory range always ends at FFFFFh. The lower boundary is programmable.
The Upper Memory Chip Select is configured through the UMCS register (Figure 5-1).
Upper Memory Chip Select Register
The value of the UMCS register at reset is F03Bh.
Bit 15: Reserved—Set to 1.
Bits 14–12: Lower Boundary (LB2–LB0)—The LB2–LB0 bits define the lower bound of
the memory access through the UCS chip selects. The number of programmable bits has
been reduced from the eight bits in the 80C186 and 80C188 microcontrollers to three bits
in the Am186ES and Am188ES microcontrollers.
The Am186ES and Am188ES microcontrollers provide an additional block size of 512K,
which is not available on the 80C186 and 80C188 microcontrollers. Table 5-2 outlines the
possible configurations and differences with the 80C186 and 80C188 microcontrollers.
UMCS Block Size Programming Values
Memory
Block
128K
256K
512K
Size
64K
Address
Starting
C0000h
F0000h
E0000h
80000h
15
1
LB2–LB0
LB2–LB0
111b
110b
100b
000b
Chip Select Unit
0 0 0 0
Comments
Default
Not available on the 80C186 or 80C188 microcontroller
DA
7
0 1 1 1
R2
R1–R0
0