Display board
U902 is the display microco
ntroller that controls the VFD (vacuum fluorescent display)
and interprets key data. The microcontroller has four peripheral I/O ports that are used for the
various control and read functions.
Display data is serially transmitted to the microcontroller from the digital board via the TXB
line to the microcontroller PD0 terminal. In a similar manner, key data is serially sent back to
the digital board through the RXB line via PD1. The 4MHz clock for the microcontroller is
generated on the display board.
DS901 is the VFD (vacuum fluorescent display) module, which can display up to 49
characters. Each character is organized as a 5 × 7 matrix of dots or pixels and includes a long
underbar segment to act as a cursor.
The display uses a common multiplexing scheme with each character refreshed in sequence.
U90
3 and U904 are the grid drivers, and U901 and U905 are the dot drivers. Note that dot driver
and grid driver data is serially transmitted from the microcontroller (PD3 and PC1).
The VFD requires both +60VDC and 5VAC for the filaments. These VFD voltages are sup-
plied by U625, which is located on the digital board.
The front panel keys (S901-S931) are organized into a row-column matrix to minimize the
number of microcontroller peripheral lines required to read the keyboard. A key is read by
strobing the columns and reading all rows for each strobed column. Key down data is
interpreted by the display microcontroller and sent back to the main microprocessor using
proprietary encoding schemes.
4-12 Troubleshooting
2410-902-01.book Page 12 Monday, November 7, 2005 2:49 PM
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