Zenith Data Systems Z-171 PC Series Service Manual page 21

Page 2-4
Installation
Table 2-1 (continued): Bus Expansion Connector Pinout
PIN NUMBER
44
45
46
47
48
49
50
51
SIGNAL NAME
GND
NC
GND
GND
MEMW*
MEMR*
lIOW*
IOR*
DMACK3*
DMARQ3
DMACK]*
DMARQI1
DMACK0*
CLK
DESCRIPTION
Address bit 7.
Address bit 6.
Address bit 5.
Address bit 4.
Address bit 3.
Address bit 2.
Address bit 1.
Address bit 0.
Ground.
When high, resets or initializes system
logic.
+5 VDC bus.
Interrupt request 2. Used by the real-time
clock.
Ground.
DMA request 2. Assigned to floppy disk
controller.
Ground.
No connection.
Ground.
Ground.
Memory write. When low, causes data on
data bus to be stored in memory.
Memory read. When low, causes memory
to drive data onto the data bus.
1/0 write. When low, instructs an I/O device
to read data on the data bus.
I/O read. When low, instructs I/O device
to drive its data onto the data bus.
DMA acknowledge 3. Assigned to external
drive controller.
DMA request 3. Assigned to external drive
controller.
DMA acknowledge. Available for user as-
signment.
DMA request 1. Available for user assign-
ment
DMA acknowledge 0. Assigned for timer
number 1. Initiates memory refresh.
4.77 mHz system clock.