U1 Output Ports Bo Through B3; Multiplexer (U4); Cathode Drivers (V5, V6) - Watkins-Johnson Company WJ-8718A/MFP Instruction Supplement

WJ-8718A/MFP TABLE 3-4
3.1.3.4.3
Ul Output Ports BO Through B3
The BO through B3 lines provide a BCD code to display driver U3, described in
paragraph 3.1.3.8. The lines are synchronized to the scan lines, allowing U1 to automatically
scan the switches and update or refresh the front panel displays.
3.1.3.5
Column Driver (U11)
Integrated circuit Ull is a 3-to-8 line decoder. The Gl, G2A, and G2B enable
inputs are tied to +5 Vdc and ground to hold the decoder in the enabled state. The levels on the
A, B, and C inputs are decoded to provide a low level on one Y output as listed in Table 3-4.
Refer to paragraph 3.1.3.4.2 for details of the function of the Y outputs.
3.1.3.6
Multiplexer (U4)
U4 is a 4-to-16 line decoder. The SLO through SL3 lines from Ul count in BCD as
the front panel Group 1 switches are scanned. The BCD code is applied across pull-up resistors
Rll through R14 to the A, B, C, and D select inputs of U4. Multiplexer U4 is a single digitally
controlled 16-channel switch, arranged so that the 4-bit BCD input selects the channel
associated with the code, as listed in Table 3-5, the U4 Truth Table.
3.1.3.7
Cathode Drivers (U5, U6)
The outputs of multiplexer U4 are connected to the D inputs of cathode drivers U5
and U6. The output of the selected U4 channel goes high, and U5 or U6 inverts the high D input
to a low level which is applied to the cathode of the selected LED or LED array. The display
digits are enabled one at a time and refreshed at a rate undetectable by the human eye.
Table 3-4. U11 Truth Table
Inputs Outputs
Enable
Select
Gl G2A G2B C B A
YO
Yl Y2 Y3 Y4 Y5 Y6 Y7
1
0
0 0 0 0 0
1
1
1 1 1
1 1
1 0 0 0 0
1
1
0
1 1 1
1
1 1
1 0 0 0
1 0 1 1 0 1 1 1 1 1
1 0 0 0
1 1 1
1 1
0
1 1
1 1
1 0 0
1
0 0
1 1 1 1 0 1 1 1
1
0
0 1
0
1 1 1 1
1
1
O·
1 1
1 0 0 1 1 0
1 1
1 1 1 1
·0
1
1
0
0 1 1 1 1 1 1 1 1 1 1 0
3-13