Service manual

3.16 TP0332/2
The KEY_DET3 voltage generated by the different keys is as follows:
(1) If the PTT is pressed, KEY_DET3 voltage will still be at 0V
(2) If SIDE_KEY1 or SIDE_KEY2 is pressed, each side key generates a unique KEY_DET3 voltage by
virtue of resistors in series with each key (R12, R11, R81) in combination with R15
(3) If the ALARM key is pressed, analogue switch IC3 forces KEY_DET3 voltage to the same voltage as
the AF_PSU.
The MMI keypad keys generate unique KEY_DET3 voltages. This is described in the section below
on the “MMI Display and Keypad”.
MMI Display and Keypad (not fitted on SRP8010)
Table 3.6 MMI Connector Signal Names and Usage
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.
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 which 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 which initiated the interrupt identifies which column the key press is in.
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 keypress 0V to 5V
AF_PSU Supply 5V nominal
0VA Ground 0V
nWR Write line (for future use) 0V write, 5V read