EISA System Architecture

EXRDY	input/output	EISA Ready. Set inactive by the currently addressed
		EISA slave if it requires more time to complete a bus
		cycle. Controlled by the EBC when an EISA bus mas-
		ter is addressing an ISA or host slave and under some
		conditions when data bus steering is necessary.
MSBURST#	input/output	Master Burst. Generated by an EISA or host master
		(through the EBC) when the addressed slave has indi-
		cated it supports burst bus cycles by asserting
		SLBURST#. Set active by the EISA master or the EBC
		at the midpoint of the first data time and sampled by
		the slave at the end of the first data time.
SLBURST#	input	Slave Burst. Used by the currently addressed EISA
		slave to indicate it supports burst bus cycles. Sampled
		by the master at the end of address time.
EX32#	input/output	EISA Size 32. Generated by the currently addressed
		slave if it is a 32-bit EISA slave. Generated by the EBC
		at the end of data bus steering to signal return of bus
		cycle control to the EISA bus master. Also generated
		by the EBC if an EISA bus master addresses a host
		slave (HLOCMEM# or HLOCIO# sampled active be
		EBC).
EX16#	input/output	EISA Size 16. Generated by the currently addressed
		slave if it is a 16-bit EISA slave. Generated by the EBC
		at the end of data bus steering to signal return of bus
		cycle control to the EISA bus master. Also generated
		by the EBC if an EISA bus master addresses a host
		slave (HLOCMEM# or HLOCIO# sampled active be
		EBC).

Cache Support

The EBC provides two output signals to support bus snooping. HSSTRB# is used in 386/82385 host CPU systems, while QHSSTRB# is used in 486 host CPU systems. These signals indicate to a system cache controller that a bus master is writing to system memory. The RDE#, or Ready Delay Enable, input instructs the cache support unit in the EBC to add a wait state by delaying HERDYO# and HRDYO# during a host to EISA/ISA read to allow increased cache SRAM write data setup time during cache read miss bus cycles.

Reset Control

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Chapter 12: Intel 82350DT EISA Chipset

Table 12-9 describes the signals associated with the EBC's Reset Control unit (see figure 12-2).

Table 12-9. The EBC's Reset Control Interface Signals

	Signal			Direction			Description
	RST			out			System Reset. Remains active until 10 microseconds after
							SPWROK goes active. Resets major system components to
							a known state.
	RSTCPU			out			Reset Host CPU. Driven active when: power isn't stable
							(SPWROK inactive); a shutdown bus cycle is detected on
							the host bus; or RSTAR# is sensed active. See RSTAR# de-
							scription. RSTCPU resets just the host CPU.
	RST385			out			Reset 385 cache controller. Driven active under the same
							conditions as RSTCPU. Resets the host bus cache control-
							ler, clearing all tag valid bits. In other words, the cache is
							flushed.
	RSTAR#			in			Restart. Generated under software control by: issuing a
							CPU reset command to the keyboard controller; or tog-
							gling the fast hot reset bit in the PS/2 compatibility port at
							I/O port 92h. Used by 286-specific code to reset the 286
							and return it to real mode from protected mode.
	SPWROK			in			System Power OK. Provided as an output from the power
							supply. When inactive, the Reset Control unit sets
							RSTCPU, RST385 and RST active.

Slot-Specific I/O Support

During I/O bus cycles, the EBC generates a pulse on the signal AENLE#, AEN Latch Enable. This is used by the AEN logic to latch the active AENx line. For more information on slot-specific I/O support and AEN decode, refer to the chapter entitled “EISA System Configuration.”

Clock Generator Unit

Table 12-10 provides a description of the signals related to the EBC's Clock Generator unit.

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EISA System Architecture

Table 12-10. EBC's Clock Generation Unit Signal Description

	Signals			Direction			Description
	HCLKCPU			in			Host CPU Clock.
	BCLK			out			Bus Clock. BCLK is generated by dividing the
							HCLKCPU input clock by a factor determined by the
							CPU[3:0] inputs. For a 25MHz 386 or 486 host CPU, the
							BCLK frequency will be 8.33MHz. For a 33MHz 386 or
							486, the BCLK frequency will be 8.25MHz.
	CLKKB			out			Keyboard Clock. The EBC's Clock Generation unit pro-
							vides an output clock for the keyboard controller. Its fre-
							quency is derived by dividing the HCLKCPU input by a
							factor determined by the CPU[3:0] inputs. If the host
							CPU is a 25MHz 386, the CLKKB output frequency will
							be 10MHz. If the host CPU is a 25MHz 486, the CLKKB
							output frequency will be 8.33MHz. If the host CPU is a
							33MHz 386 or 486, the CLKKB output frequency will be
							11MHz.
	BCLKIN			in			Bus Clock input. Allows the EBC to monitor the BCLK
							signal.

I/O Recovery

The ISA bus's default ready timer built into the EBC automatically forces accesses to 8 or 16-bit ISA I/O devices to append one wait state to the bus cycle. If a delay of longer than one wait state is desired, the signal LIOWAIT#, Long I/O Wait, may be asserted to provide a maximum of eleven wait states when accessing 8-bit ISA I/O slaves or three wait states when accessing 16-bit ISA I/O slaves.

Testing

Normally pulled high with an external pullup resistor, an active level on the TEST1# input causes the EBC to float all of its outputs except BCLK. This allows a board tester to gain control of all of the output signal lines for testing purposes.

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