U2 Scan Line Outputs/Return Line Inputs; U2 Output Ports Bo Through B3; Column Driver (U12); Multiplexer (U8) - Watkins-Johnson Company WJ-8718A/MFP Instruction Supplement

WJ-8718A/MFP CIRCUIT DESCRIPTION
3.1.3.9.2
U2 Scan Line Outputs/Return Line Inputs
The internal circuits of U2 provide a binary-coded count on the SLO through SL3
output lines. Three bits of the binary code (0 through 7) are decoded by U12 (described in
paragraph 3.1.3.10) to become the column scan lines (BCO through BC7). Each column scan line
is connected to one of eight
X
planes in the Group 2 switch matrix. Each sWitch in the matrix
is located at a point where the
X
and
Y
planes cross and can be identified by the unique position
it occupies. The
Y
planes of the matrix are connected to the return lines (RLO through RL7) of
U2. When a switch is closed, a circuit is completed from the column scan line, through the
closed switch, and through the return (row scan) line back to U2. The closed switch position is
coded and stored in U2 RAM. During the execution of its program, the microprocessor initiates
any further action necessary to incorporate the functions of the closed switch.
The binary count (0 through 15) on the 8LO through SL3 lines is also applied, to
multiplexer U8, where one of 16 channels is switched as the count proceeds (r.efer to
paragraph 3.1.3.11). The resultant high output from U8 results (through U9 and U10) in a
negative cathode voltage to a front panel LED indicator or display array (see
paragraphs 3.1.2.2.3 and 3.1.2.2.4). The LED, however, is not forward biased, and does not
illuminate, unless its anode is sufficiently more positive than the cathode. The anode drive is
provided through the BO through B3 outputs of U2, described in the following paragraph.
3.1.3.9.3
U2 Output Ports BO Through B3
The BO through B3 lines provide a BCD code to display driver U7, described in
paragraph 3.1.3.13. The lines are synchronized to the scan lines, allowing U2 to automatically
scan the switches and update or refresh the front panel address displays. In addition, the BCD
output can be programmed by the microprocessor to reflect the data from a monitored receiver
or the contents of a recalled memory channel.
3.1.3.10
Column Driver (U12)
Integrated circuit U12 is identical to Ul1, described in paragraph 3.1.3.5. Refer to
paragraph 3.1.3.9.2 for a discussion of the functions of the
Y
outputs.
3.1.3.11
Multiplexer (U8)
Multiplexer U8 functions identically to U4, described in paragraph 3.1.3.6. The U8
multiplexer is associated with the Group 2 keyboard/display interface, U2.
3.1.3.12 Cathode Drivers (U9, U10)
Cathode drivers U9 and U10 function identically to U5 and U6, described in
paragraph 3.1.3.7. U9 and U10 are associated with the Group 2 keyboard/display interface, U2.
3-15