User`s guide

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3-11
3.13.3 PC/104 CHANNEL SIGNAL DESCRIPTION
Name I/O Description
BUSCLK [Output] The BUSCLK signal of the I/O channel is asynchronous to the CPU clock.
RSTDRV [Output] This signal goes high during power-up, low line-voltage or hardware reset
SA0 – SA19 [Input / Output] The System Address lines run from bit 0 to 19. They are latched onto the falling
edge of "BALE"
LA17 - LA23 [Input / Output] The Unlatched Address line run from bit 17 to 23
SD0 - SD15 [Input / Output] System Data bit 0 to 15
BALE [Output] The Buffered Address Latch Enable is used to latch SA0 - SA19 onto the falling
edge. This signal is forced high during DMA cycles
-IOCHCK [Input] The I/O Channel Check is an active low signal which indicates that a parity error
exist on the I/O board
IOCHRDY [Input, Open collector] This signal lengthens the I/O, or memory read/write cycle, and should be held low
with a valid address
IRQ 3-7, 9-12,
14, 15
[Input] The Interrupt Request signal indicates I/O service request attention. They are
prioritized in the following sequence : (Highest) IRQ 9, 10, 11, 12, 13, 15, 3, 4, 5,
6, 7 (Lowest)
-IOR [Input / Output] The I/O Read signal is an active low signal which instructs the I/O device to drive
its data onto the data bus
-IOW [Input / Output] The I/O write signal is an active low signal which instructs the I/O device to read
data from the data bus
-SMEMR [Output] The System Memory Read is low while any of the low 1 Mbytes of memory are
being used
-MEMR [Input / Output] The Memory Read signal is low while any memory location is being read
-SMEMW [Output] The System Memory Write is low while any of the low 1 Mbytes of memory is
being written
-MEMW [Input / Output] The Memory Write signal is low while any memory location is being written
DRQ 0-3, 5-7 [Input] DMA Request channels 0 to 3 are for 8-bit data transfers. DMA Request channels
5 to 7 are for 16-bit data transfers. DMA request should be held high until the
corresponding DMA has been completed. DMA request priority is in the following
sequence:(Highest) DRQ 0, 1, 2, 3, 5, 6, 7 (Lowest)
-DACK 0-3, 5-7 [Output] The DMA Acknowledges 0 to 3, 5 to 7 are the corresponding acknowledge signals
for DRQ 0 to 3 and 5 to 7
AEN [Output] The DMA Address Enable is high when the DMA controller is driving the address
bus. It is low when the CPU is driving the address bus
-REFRESH [Input / Output] This signal is used to indicate a memory refresh cycle and can be driven by the
microprocessor on the I/O channel
TC [Output] Terminal Count provides a pulse when the terminal count for any DMA channel is
reached
SBHE [Input / Output] The System Bus High Enable indicates the high byte SD8 - SD15 on the data bus
-MASTER [Input] The MASTER is the signal from the I/O processor which gains control as the
master and should be held low for a maximum of 15 microseconds or system
memory may be lost due to the lack of refresh
-MEMCS16 [Input, Open collector] The Memory Chip Select 16 indicates that the present data transfer is a 1-wait
state, 16-bit data memory operation
-IOCS16 [Input, Open collector] The I/O Chip Select 16 indicates that the present data transfer is a 1-wait state,
16-bit data I/O operation
OSC [Output] The Oscillator is a 14.31818 MHz signal
-ZWS [Input, Open collector] The Zero Wait State indicates to the microprocessor that the present bus cycle
can be completed without inserting additional wait cycle
Table 3-9 I/O Channel Signal Description