
Chip Select Unit
5-4
5.5.1
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).
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.
Table 5-2
UMCS Block Size Programming Values
Memory
Block
Size
Starting
Address
LB2–LB0
Comments
64K
F0000h
111b
Default
128K
E0000h
110b
256K
C0000h
100b
512K
80000h
000b
Not available on the 80C186 or 80C188 microcontroller
15
7
0
LB2–LB0
1
0 0 0 0
R1–R0
0
1 1 1
R2
DA
Содержание Am186 ES
Страница 1: ...Am186 ES and Am188 ES User s Manual...
Страница 4: ...iv...
Страница 12: ...Table of Contents xii...
Страница 22: ...Features and Performance 1 8...
Страница 60: ...System Overview 3 28...
Страница 84: ...Chip Select Unit 5 14...
Страница 132: ...Timer Control Unit 8 8...
Страница 166: ...Programmable I O Pins 11 6...
Страница 184: ...Register Summary A 18...