CHIP-SELECT UNIT

Register Name:MCS and PCS Alternate Control Register

Register Mnemonic:

MPCS

Register Function:Controls operation of the MCS and PCS chip- selects.

15

 

M

M

M

 

6

5

4

 

 

 

 

MM

3 2

MM

1 0

EM X S

 

 

 

0

 

R

R

R

 

2

1

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A1144-0A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bit

 

Bit Name

Reset

 

 

Function

 

Mnemonic

 

State

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

M6:0

 

Block Size

XXH

Defines the block size for the MCS chip-selects.

 

 

 

 

 

 

Table 6-5 on page 6-14 lists allowable values.

 

 

 

 

 

 

 

 

 

 

 

 

 

EX

 

Pin Selector

XH

Setting EX configures

 

 

 

 

 

as chip-selects.

 

PCS6:5

 

 

 

 

 

Clearing EX configures the pins as latched

 

 

 

 

 

 

address bits A2:A1.

 

 

 

 

 

 

 

 

 

 

 

MS

 

Bus Cycle

XH

Clearing MS activates

 

 

 

 

for I/O bus

 

PCS6:0

 

 

Selector

 

cycles. Setting MS activates

PCS6:0

for

 

 

 

 

 

 

memory bus cycles.

 

 

 

 

 

 

 

 

 

 

R2

 

Bus Ready

X

Applies only to

 

 

 

 

When R2 is clear, bus

 

 

PCS6:4.

 

 

Disable for

 

ready must be active to complete a bus cycle.

 

 

 

PCS6:4

 

 

When R2 is set, R1:0 control the number of bus

 

 

 

 

 

 

wait states and bus ready is ignored.

 

 

 

 

 

 

 

 

R1:0

Wait State

3H

Apply only to

 

 

R1:0 define the minimum

 

PCS6:4.

 

 

Value for

 

number of wait states inserted into the bus

 

 

 

PCS6:4

 

 

cycle.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOTE: Reserved register bits are shown with gray shading. Reserved bits must be written to a logic zero to ensure compatibility with future Intel products. A starting address other than an integer multiple of the block size defined in this register causes unreliable chip-select operation. Reading this register and the MMCS or PACS register (before writing them) enables the associated chip-selects; however, none of the programmable fields will be properly initialized.

Figure 6-9. MPCS Register Definition

6-11

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Image 166
Intel 80C188XL, 80C186XL user manual Register NameMCS and PCS Alternate Control Register, Mpcs, X S