microcontroller in which bit 6 was set with a meaningful value would not produce the address expected on the Am186ER.

When the PCS chip selects are mapped to I/O space, BA19–16 must be programmed to 0000b because the I/O address bus is only 16-bits wide.

 

 

 

 

 

 

Table 5-5

PCS Address Ranges

 

 

 

 

 

 

 

 

 

 

Line

Range

 

PCS

 

 

 

Low

High

 

 

 

 

 

 

 

 

 

 

 

 

Base Address

Base Address+255

 

PCS0

 

 

 

 

 

 

 

 

Base Address+256

Base Address+511

 

PCS1

 

 

 

 

 

 

 

 

Base Address+512

Base Address+767

 

PCS2

 

 

 

 

 

 

 

 

Base Address+768

Base Address+1023

 

PCS3

 

 

 

 

 

Reserved

N/A

N/A

 

 

 

 

 

 

 

 

Base Address+1280

Base Address+1535

 

PCS5

 

 

 

 

 

 

 

 

Base Address+1536

Base Address+1791

 

PCS6

 

 

 

 

 

 

Bits 6–4: Reserved —Set to 1.

Bit 3: Wait-State Value (R3)—If this bit is set to 0, the number of wait states from zero to three is encoded in the R1–R0 bits. In this case, R1–R0 encodes from zero (00b) to three (11b) wait states.

When R3 is set to 1, the four possible values of R1–R0 encode four additional wait-state values as follows: 00b = 5 wait states, 01b = 7 wait states, 10b = 9 wait states, and 11b = 15 wait states. Table 5-6shows the wait-state encoding.

Table 5-6 PCS3–PCS0 Wait-State Encoding

R3

R1

R0

Wait States

 

 

 

 

0

0

0

0

 

 

 

 

0

0

1

1

 

 

 

 

0

1

0

2

 

 

 

 

0

1

1

3

 

 

 

 

1

0

0

5

 

 

 

 

1

0

1

7

 

 

 

 

1

1

0

9

 

 

 

 

1

1

1

15

 

 

 

 

Bit 2: Ready Mode (R2)—The R2 bit is used to configure the Ready mode for the PCS 3– PCS0 chip selects. If R2 is set to 0, external ready is required. External ready is ignored when R2 is set to 1. In each case, the processor also uses the value of the R3 and R1–R0 bits to determine the number of wait states to insert. The Ready mode for PCS6–PCS5 is configured through the MPCS Register.

Bits 1–0:Wait-State Value (R1–R0)—The value of R3 and R1–R0 determines the number of wait states inserted into a PCS3–PCS0 access. Up to 15 wait states can be inserted. See the discussion of bit 3 (R3) for the wait-state encoding of R1–R0.

From zero to three wait states for the PCS6–PCS5 outputs are programmed through the R1–R0 bits in the MPCS Register.

Chip Select Unit

5-13

Page 81
Image 81
AMD Am188TMER Bits 6-4 Reserved -Set to, PCS Address Ranges Line, Low High, PCS3-PCS0 Wait-State Encoding Wait States