AM186ES Advanced Micro Devices, AM186ES Datasheet - Page 75

• 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

Bits 11–8: Reserved
Bit 7: Disable Address (DA)—The DA bit enables or disables the AD15–AD0 bus during
the address phase of a bus cycle when UCS is asserted. If DA is set to 1, AD15–AD0 is
not driven during the address phase of a bus cycle when UCS is asserted. If DA is set to
0, AD15–AD0 is driven during the address phase of a bus cycle. Disabling AD15–AD0
reduces power consumption. DA defaults to 0 at power-on reset.
Note: On the Am188ES microcontroller, the AO15–AO8 address pins are driven during
the data phase of the bus cycles, even when DA is set to 1 in either the Upper Memory
Chip Select register (UMCS) or the Low Memory Chip Select register (LMCS).
If BHE/ADEN (on the 186) or RFSH2/ADEN (on the 188) is held Low on the rising edge of
RES, then AD15–AD0 is always driven regardless of the DA setting. This configures AD15–
AD0 to be enabled regardless of the setting of DA.
If BHE/ADEN (on the 186) or RFSH2/ADEN (on the 188) is High on the rising edge of RES,
then DA in the Upper Memory Chip Select (UMCS) register and DA in the Low Memory
Chip Select (LMCS) register control the AD15–AD0 disabling.
See the descriptions of the BHE/ADEN and RFSH2/ADEN pins in Chapter 3.
Bit 6: Reserved—Set to 0.
Bits 5–3: Reserved—Set to 1.
Bit 2: Ready Mode (R2)—The R2 bit is used to configure the ready mode for the UCS chip
select. If R2 is set to 0, external ready is required. If R2 is set to 1, external ready is ignored.
In each case, the processor also uses the value of the R1–R0 bits to determine the number
of wait states to insert. R2 defaults to 0 at reset.
Bits 1–0: Wait-State Value (R1–R0)—The value of R1–R0 determines the number of wait
states inserted into an access to the UCS memory area. From zero to three wait states can
be inserted (R1–R0 = 00b to 11b). R1–R0 default to 11b at reset.
Chip Select Unit
5-5