Zenith Z-171 Series Service Manual page 21

Page
2-4
Installation
Table 2-1 (continued): Bus Expansion Connector Pinout
PIN NUMBER
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
SIGNAL NAME
A7
A6
A5
A4
A3
A2
Al
AO
GND
DRVRST
+5VDC
IRQ2
GND
DRQ2
GND
NC
GND
GND
MEMW*
MEMR*
10W*
10R*
DMACK3*
DMARQ3
DMACKl*
DMARQl
DMACKO*
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 O.
Ground.
When high, resets or initializes system
logic.
+5 VDCbus.
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 VO device
to read data on the data bus.
VO read. When low, instructs VO 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 O. Assigned for timer
number 1. Initiates memory refresh.
4.77 mHz system clock.