Intel 80C186XL, 80C188XL user manual 6.4PROGRAMMING, 6.4.1Initialization Sequence

CHIP-SELECT UNIT

6.4PROGRAMMING

Four registers determine the operating characteristics of the chip-selects. The Peripheral Control Block defines the location of the Chip-Select Unit registers. Table 6-1 lists the registers and their associated programming names.

Table 6-1. Chip-Select Unit Registers

Control Register	Alternate Register	Chip-Select Affected
Mnemonic	Mnemonic
UMCS	None
				UCS
LMCS	None
				LCS
MMCS	MPCS
			MCS3:0
PACS	MPCS
			PCS6:0

The control registers (Figures 6-5 through 6-7) define the base address and bus ready and wait state requirements for the corresponding chip-selects. The alternate control register (Figure 6-9) defines the block size for MCS3:0. It also selects memory or I/O space for PCS6:0, selects the function of the PCS6:5 pins, and defines the bus ready and wait state requirements for PCS6:4.

6.4.1Initialization Sequence

Chip-selects do not have to be initialized in any specific order. However, the following guidelines help prevent a system failure.

1.Initialize local memory chip-selects

2.Initialize local peripheral chip-selects

3.Perform local diagnostics

4.Initialize off-board memory and peripheral chip-selects

5.Complete system diagnostics

An unmasked interrupt or NMI must not occur until the interrupt vector addresses have been writ- ten to memory. Failure to prevent an interrupt from occurring during initialization will cause a system failure. Use external logic to generate the chip-select if interrupts cannot be masked prior to initialization.

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