Theory of Operation of the Shaq 27722-1 (A23) LED Display Board (4-player score board).Theory of Operation of the Shaq 27722-1 (A23) LED Display Board (4-player score board).
Theory of Operation
This is a brief technical introduction to the operation of the 27722-1 (A23) board. It will cover inputs and behavior of the board.
Inputs
This board accepts the following three control inputs:
- Master Reset (/MR)
- 8-Bit Data (DX0–DX7 – pulled up to +5v/VCC)
- Enable/Strobe for the latches (AX4)
It also accepts +5, common GND, +12 and the +12V GND (both GNDs are connected together).
The incoming 8-bit data is split into two 4-bit words with the low word (DX0–DX3) used for specifying the value to display on a particular LED digit via the ‘4511 (BCD to 7-segment latch/decoder/driver), with DX0, DX1, DX2 and DX3 connected to inputs A, B, C and D (or D1, D2, D3, and D4), respectively. The high word (DX4–DX7) is used for digit selection via the ‘4514 (4 to 16-Line Latch/Decoder/Demultiplexer), with DX4, DX5, DX6 and DX7 connected to inputs A, B, C and D, respectively.
Latches for the corresponding chips are controlled via the AX4 signal, which is directly connected to the 4511’s /LE input and also goes through an inverter whose output is connected to the 4514’s LE.
The /MR signal is connected to the 4511’s /BI signal, which is used to blank the displays whenever the game is in reset.
Continue reading Theory of Operation of the Shaq 27722-1 (A23) LED Display Board