Control Board Address
Decoding
Key Scanning
Display Driving
Address decoding for the control board functions is partially carried
out on the microprocessor board. Address lines A3-A9 and A14 are
passed through latch U18 under the control of sub-decoder 2 (U14).
A14 then becomes the MODE control for the display driver (refer
to "Display Driving" ) , while A3-A9 pass through bus driver U21 .
Decoder U l 7 uses A 6 and A 7 t o produce the "write select" signals
WS 1-WS6 and the WRITE signal to the display driver (refer to
"Display Driving" ) .
Refer t o Figure 10. 7-6 and Figure 1 0 . 7-7 The keyboard assembly
A4 is a switch panel on which all mode, control, parameter,
waveform, output and trigger control pushbuttons are mounted.
The microprocessor scans the frontpanel key matrix using a BCD to
decimal converter U20 and an 8-to- l multiplexer U 1 9. A3, A4 and
A5 are the inputs to U20 and are continuously incremented from one
to six by the microprocessor. The six "decimal" outputs from U20,
KDO-KD5, are used as the vertical signal paths to the key matrix.
The horizontal signal paths of the key matrix, KSO-KS7, form the
inputs to the multiplexer U19, which is controlled by address lines
AO, Al and A2. The output from U 1 9 therefore represents the state
of the key joining the vertical signal path (addressed by A3-A5) and
the horizontal signal path (addressed by AO-A2) . Each time the
microprocessor increments the address to U20 it cycles the address to
Ul9 through all 8 horizontal paths.
Display Driver U22
The display driver operates the key, mode, control and unit LEDs,
along with the individual digital display segments, using a matrix
technique similar to the keyboard. The outputs DIGO-DIG7 form
the vertical signal paths while the outputs a-g and DP form the
horizontal paths. The display driver contains 8 bytes of RAM which
store 8 data bits (a-g and DP) to be used with each of the 8 "digit"
outputs DIGO-DIG7.
The MODE signal determines whether the display driver interprets
data as control instructions or display data to be stored in RAM:
Table 1 0.7-1 . Display Driver Control Signals
Signal
Pin Status
ODE
M
9
HIGH Load control instruction on WRITE pulse
LOW Load display data on WRITE pulse
WRITE
8
HIGH Data not loaded
LOW Data loaded
Servicing the Microprocessor and Front-panel 1o.7 -5
Function