Datascope System 98 Service Manual page 154

2.3.4 Keypad Controller (0670-00-0645)
The Keypad Controller board provides the System 98 with the following
functions:
- Detecting, debouncing and reporting any keystroke activated by an operator at
< the keypad.
- Detecting and reporting the position of Inflate and Deflate potentiometers as
activated by the operator.
- Activating LEDs residing on the keypad.
- Passing Video signals to the Video Receiver Board.
- DC/DC Converter to supply +5V and +12V to power the monitor module.
The Keypad Controller board is based upon the Motorola MC68HC711
microcontroller. Features include: 12 K bytes of EPROM, 512 bytes of
electrically erasable programmable ROM (EEPROM), and 512 bytes of RAM.
The MC68HC711E9 (U1) is operating in a single-chip mode with no external
address or data bus available. Port A is used as an input port. Port B serves as an
output port to activate the Keypad row drivers. Port C is used as an input port to
read back the Keypad column data. Port D serves as the serial communication
interface (SCI) and serial peripheral interface (SPI). The SCI serves as a data link
between the Keypad Controller and Main board. The SPI provides a
communication link berween the MC68HC711 and the LED display driver based
upon National Semiconductor MM5451 (U6).
The MM5451 is specifically designed to operate LED displays with minimal
interface with the display and data sources. Serial data transfer from the
microcontroller is accomplished with 2 signals, serial data and clock. Using a
format of leading "1" followed by 35 data bits allows data transfers without an
additional write signal. The 35 data bits are latched after rhe 36th bit is complete,
thus providing non-multiplexed, direct drive to the display. Outputs change only
if the serial data bits differ from the previous data.
There are 36 LEDs mounted onto the keypad. In addition there are 10 more LEDs
arranged into a bar graph assembly, representing the Augmentation LED indicator.
The LED Bar Graph is mounted directly into the Monitor Keypad Controller
board. Table 1 represents LED functional and numerical cross references with
LED number corresponding to the serial data bit number. LEDs 0 through 17 are
controlled by US and LEDs 18 through 35 are controlled by U4. The 10 LED
Augmentation bar graph is controlled by U4.