FIRMWARE SIGNATURE ANALYSIS-
KEYBOARD ENCODER
(U1421)
I. Purpose
To provide a complete checkout of the keyboard encoder, front panel pushbuttons and signal lines to
aid in troubleshooting key entry problems.
11.
Equipment required
A. Tektronix SA 501 Signature Analyzer (or equivalent)
6.
Two TM 500 Flexible Extenders, Tektronix Part Number 067-0645-02
C. 16-pin DIP clip, Tektronix Part Number 003-0709-00
Ill.
Electrical conditions necessary to perform tests
A.
CPU, ROM, RAM, data and address bus working properly (verified by power-up self test)
6.
Sel keyboard (U1311, pin 13) working. Check U1311 pin 13 for pulses. Approximately 5.5 ms
apart.
IV.
Setup
A. PS 5010 (on extenders)
1. Set mode jumper (J1320) as shown.
IT]
Signature
mode
2. Set runlforce data jumper (J1220) as shown.
8.
Signature analyzer
Connect to CPU board and set as follows:
Threshold
=
TTL
Start
=
I
Connect to U1311, pin 13 via DIP clip
Stop
=
I
Connect to U1311, pin 13 via DIP clip
Clock
=
I
Connect to ($2 via Jl 1 1 1, pin 2 (clock)
Gnd
=
Connect to ground test point (TP1011)
V.
Measurements
Using the following chart, verify stimulus and response for each front panel key. Start by verifying
+
5
V
signature, then push the problem button(s) and read data bus at U1211, pins 1-8 for correct
code. Note that data bits 0, 1, and 2 are not affected by keyboard encoder.
If incorrect data is received check the states of the
X
and
Y
inputs to U1421 (keyboard encoder)
according to those in the chart.
X
is a pulse (approximately 1-5 ms);
Y
is a low as long as the key
is down. Whenever a key is down, U1421, pin 13 (data available) is high. When key is released this
signal should go low.
Continued on following page.
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