Service manual

Page 20
SVR-200 Service Manual
T0 Test input, active low. Shorting J3 puts the microprocessor into test mode for alignment purposes. If
shorted at power up, the receiver will operate open squelch mode and audio will be heard at the local
speaker port regardless of carrier or tone input to the receiver. Although alignment is normally done
with the RSSI output at TP1, a Sinad reading can be obtained using this mode of the test input. All
other functions of the SVR-200 are disabled in this mode and power will have to be turned off then
on to reset the unit.
If J3 is shorted after power has been applied, the microprocessor will enter the lock tone test mode,
key the repeater and send the programmed lock tone for as long as J3 is shorted. Remove the short
from J3 to return to normal operation.
T1 On-air detect input. The on-air detect line (P1 pin 9) is used to detect local mic PTT from the mobile,
and in trunking mode, this line is used to detect that the mobile transmitter is actually on the air. The
input is buffered by Q10 and the polarity of the signal is determined by PC programming.
WR Turns the Rx 5V line on or off to the RF PCB.
RD Detects the version of RF PCB installed (UHF only).
TXD Transmit data output for programming. Data is sent to the PC on this line at 300 baud, 8 data bits, 1
stop bit and no parity. This line is active only during programming mode.
RXD Receive data input for programming. Data is received from the PC on this line at 300 baud, 8 data
bits, 1 stop bit and no parity. This line is also used to sense when the programming cable is inserted.
If RXD is grounded, the SVR-200 operates in the normal mode. If this line is high, programming mode
is entered and the OPT LED is on continuously.
Reset Active high input to reset the microprocessor. U11 provides a 350mSec delayed high signal to this pin
during power up or if the 5V line falls below 4.5VDC.
Xtal The microprocessor uses a 4.032MHz xtal for all of the timing and program execution clock cycles.
The output of the on board oscillator also drives the xtal input to U5. The output of U5 xtal oscillator
drives the input of U4.