Sailor RM2042 Technical Manual page 65

5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS RM2042
Output pin PB4 is used to control a remote alarm circuit.
Output pin PB5 is used to control the relay on the interface module.
Output pin PB6 is used to control output from the syncronus transmitter U26, and the modem IC on the
receiver module. A logic low level starts the transmission, and a logical high level ends the transmission.
Output pin PB7 is used to control the generation of alarm tones by U21.1. A logical low disables, and a
logical high enables the output from U21.1.
Input pin PC0 is used to determine the status of the key input from the PTT.
Input pin PC1 is used to determine the status of the carrier detect.
Input pin PC2 is the serial bus interrupt request from the connected VHF.
Input pin PC3 is a signal from the power fail circuit, telling that VBAT is dropping below 10V.
4.9152 MHz OSCILLATOR WITH DIVIDER
The 4.9152 MHz oscillator is build as a gate oscillator around U16, with the crystal X2 to control the
oscillation frequency. The oscillator is used as a reference clock for the divider that generates baud rates
for syncronus and asyncronus communication.
PRINTER STROBE GENERATOR
When the STRB(P27) signal from the interface module goes low, U14.2 generates, after delay of 2 s, a
U
4 s logic low strobe pulse to the printer (STROBE (LPT)).
U
MODEM COMMUNICATION INTERFACE
The modem communication interface U26, is a syncronus 1200 baud receiver/transmitter. The receiver
is controlled by a an external SYNC signal, and a syncronus sampling clock. The SYNC signal is the
MODULATION DETECT signal from the channel-70 receiver. When this signal goes high, and the first
high going edge on RXDATA is detected, the syncronus receiver clock is started and RXDATA is sampled.
Each bit is sampled 8 times (RXCLX is 9600 Hz), and whenever one bit is received, RXRDY goes high,
and the microprocessor is interrupted. Data is then fetched by the microprocessor, for further processing.
U26 converts data it receives via the parallel data bus to serial data. The data is output on TXDATA, if/
when the CTS input pin is low. Whenever the U26 is ready to send another byte, TXRDY goes high and
interrupts the microprocessor. If the microprocessor has more data to send, another byte is written to U26.
Transmission is disabled by setting the CTS input high.
VOLTAGE CONVERTER
The voltage converter U32 is used to generate -5V from the +5V supply. The -5V is used to control the
view angle of the lcd dot-matrix display.
KEYBOARD LIGHT ON/OFF
The two transistors Q2 and Q3 are used to control the keyboard light. When PB0 on U22 is high Q2 and
Q3 is on, and VBAT is supplied to the LED's on the keyboard module.
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