A/d reference, Bus_port – Motorola CMD11E1 User Manual
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BUS_PORT
The BUS_PORT supports off-board parallel devices. Power (+5V), ground, address lines, data
lines, and control lines are brought out to this 34 pin connector. Pin assignments are as follows:
PIN
BUS_PORT
PIN
GND
1
¨ ¡
2
D3
D2
3
¡ ¡
4
D4
D1
5
¡ ¡
6
D5
D0
7
¡ ¡
8
D6
A0
9
¡ ¡
10
D7
A1
11
¡ ¡
12
A2
A10
13
¡ ¡
14
A3
OE
15
¡ ¡
16
A4
A11
17
¡ ¡
18
A5
A9
19
¡ ¡
20
A6
A8
21
¡ ¡
22
A7
A12
23
¡ ¡
24
A13
W/R
25
¡ ¡
26
CS0
CS1
27
¡ ¡
28
CS2
CS3
29
¡ ¡
30
CS4
CS5
31
¡ ¡
32
IRQ
+5
33
¡ ¡
34
M2
A/D REFERENCE
The VRH and VRL lines from the HC11 are connected to +5v through R3 and to ground through
R2 respectively. These two resistors are located next to the MCU_PORT header. The resistors
are identified on the silk screen by their reference designators. The appropriate resistor(s) need to
be removed in order to apply an external reference to the VRH and/or VRL inputs.