Intel 80C186XL, 80C188XL user manual 7.8REFRESH OPERATION AND BUS HOLD, Refresh Control Unit

REFRESH CONTROL UNIT

	mov	dx, RFBASE	;set upper 7 address bits
	mov	ax, _dram_addr
	out	dx, al
	mov	dx, RFTIME	;set clock pre_scaler
	mov	ax, _clock_time
	out	dx, al
	mov	dx, RFCON	;Enable RCU
	mov	ax, Enable
	out	dx, al
	mov	cx, 8	;8 dummy cycles are
			;required by DRAMs
	xor	di, di	;before actual use
_exercise_ram:
	mov	word ptr [di], 0
	loop	_exercise_ram
	pop	di	;restore saved registers
	pop	dx
	pop	cx
	pop	ax
	pop	bp	;restore caller’s bp
	ret
_config_rcu	endp
lib_80186	ends
	end

Example 7-1. Initializing the Refresh Control Unit (Continued)

7.8REFRESH OPERATION AND BUS HOLD

When another bus master controls the bus, the processor keeps HLDA active as long as the HOLD input remains active. If the Refresh Control Unit generates a refresh request during bus hold, the processor drives the HLDA signal inactive, indicating to the current bus master that it wishes to regain bus control (see Figure 7-9). The BIU begins a refresh bus cycle only after the alternate master removes HOLD. The user must design the system so that the processor can re- gain bus control. If the alternate master asserts HOLD after the processor starts the refresh cycle, the CPU will relinquish control by asserting HLDA when the refresh cycle is complete.

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