CHIP-SELECT UNIT

6.4.2.4PCS Active Range

Each PCS chip-select starts at an offset above the base address programmed in the PACS register and is active for 128 bytes. The base address can start on any 1 Kbyte memory or I/O address location. Table 6-6 lists the active range for each PCS chip-select.

Table 6-6. PCS Active Range

 

 

Chip-

Active Range

 

 

 

 

 

 

Select

Start Address

Ending Address

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Base

Base + 127 (7FH)

PCS0

 

 

 

 

 

 

 

 

 

Base + 128 (080H)

Base + 255 (0FFH)

 

PCS1

 

 

 

 

 

 

 

 

 

Base + 256 (100H)

Base + 383 (17FH)

 

PCS2

 

 

 

 

 

 

 

 

 

Base + 384 (180H)

Base + 511 (1FFH)

 

PCS3

 

 

 

 

 

 

 

 

 

Base + 512 (200H)

Base + 639 (27FH)

 

PCS4

 

 

 

 

 

 

 

 

 

Base + 640 (280H)

Base + 767 (2FFH)

 

PCS5

 

 

 

 

 

 

 

 

 

Base + 768 (300H)

Base + 895 (37FH)

 

PCS6

 

 

 

 

 

 

6.4.3Bus Wait State and Ready Control

Normally, the bus ready input must be inactive at the appropriate time to insert wait states into the bus cycle. The Chip-Select Unit can ignore the state of the bus ready input to extend and com- plete the bus cycle automatically. Most memory and peripheral devices operate properly using three or fewer wait states. However, accessing such devices as a dual-port memory, an expansion bus interface, a system bus interface or remote peripheral devices can require more than three wait states to complete a bus cycle.

A three-bit field (R2:0) in the control registers defines the number of wait states and the ready requirements for the chip-selects. Figure 6-11 shows a simplified logic diagram of the wait state and ready control functions.

6-15

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Intel 80C188XL, 80C186XL user manual Bus Wait State and Ready Control, PCS Active Range