4.1 - 26 MTP700 Portable Radio / Detailed Service Manual TRANSCEIVER 400 MHz
Display and Keypad, Detailed Description
Display
The LCD (Liquid Crystal Display) Module is a Graphic Display based upon the
KS0741TB-01 display driver.
It consist of LCD Holographic Glass, LED backlight and a 22 pin flex cable connected to
the Keypad board.
The Communication to the RedCap2 IC is performed using a SPI protocol (Serial Periph-
eral Interface). The Operation of the LCD is determined upon the RS line configuration
(Data/Command).
The Display is 128X100 (Columns X Rows respectively).
Keypad
The RedCap2 processor (RCE) is responsible for decoding key presses and displaying
them properly on the LCD. The keys are arranged into a matrix of five rows and five col-
umns, which includes the Volume and PTT keys.
The PWR key is not decoded by the RCE; it directly drives the GCAP3, which sends a
signal to RCE through INT1. The five row lines are pulled high via five internal 22 Kohm
resistors. The five row lines and five column lines are fed to RedCap2 I/O pins. Pressing
any key also generates the keypad internal interrupt. The RedCap2 debounces the keys
by reading them 25 milliseconds later.
The keypad-decoding scheme works as follows:
1. RedCap2 sets rows to inputs; all columns are set as outputs and driven logic low.
2. Rows are pulled logic high. When a key is pressed, one row goes low, which indicates
a key press and sends an internal interrupt.
3. RedCap2 reads rows. A low on that row indicates a key press. All others are high.
4. RedCap2 sets all columns to output logic high.
5. One column at a time is set to output logic low. RedCap2 reads the columns to see
which one is now at a logic low level.
6. The low row level (in step 3) and low column level (in step 5) indicate the correct col-
umn and row.
All keypad circuitry is located on the keypad board. Refer to the keypad board schemat-
ics.
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