Service Manual

Page 4.10
3 ~ TECHNICAL DESCRIPTION
4.7 K
EYBOARD AND DISPLAY (MMI)
Keypad Press Detection
Electronically, the keypad keys are arranged in a matrix of 3 rows and 7 columns.
The rows are driven directly by two processor port signals KEY_ROW1 and KEY_ROW2 that are normally in
the low state. Transistors TR910-916 generate a unique voltage on KEY_DET3 for each column. Any key in the
same column generates the same voltage.
For example, if key “1” (S903) is pressed TR913 turns on and sets up a voltage on KEY_DET3 according to the
value of R932, R971 on the MMI board and R15 on the main radio board. This generates a processor interrupt
on PTT3. The processor then goes through a process of deactivating the keypad rows selectively until it
deduces which row the key press is in. The KEY_DET3 voltage that initiated the interrupt identifies which
column the key press is in.
Processor Interface to LCD Display
The LCD display is driven by LCD driver chip IC901. The driver chip interfaces to the processor via an 8-bit
data bus with the write cycle being controlled by LCD_CS and the LCD register select line controlled by
processor address line A20. The processor is only able to write to the LCD driver.
Signal Name Use Signal Type
DATA (0:7) Eight lines, processor data 0V or 5V
A(20) Low duty cycle, display address
selection
0V or 5V
BLITE Backlight enable 0V OFF, 5V ON
nLCD_CS Display enable 0V or 5V, active low
nKEY_ROW 1-2 Local keypad enables 0V or 5V, active low
KEY_DET3 Voltage proportional to key press 0V to 5V
AF_PSU Supply 5V nominal
0VA Ground 0V
nWR Write line(for future use) 0V write, 5V read
Four function keys are located below the display:
Legend Function
M
Activate menu
–
Scroll down through channels (or menu, if active)
+
Scroll up through channels (or menu, if active)
OK
Confirm choice or action (ie. Enter).
The SRP9130 has 12 additional keys (supported by the daughter board) arranged as a DTMF keypad.