Codan NGT 2010 RF Technical & Service Manual page 786

The following external devices are connected to the bus:
•
•
•
The voltage detector and reset generator IC102 resets the microprocessor if the 5 V
supply falls below 4.7 V.
Two 8-bit mode switches connected to the microprocessor input ports (pins 7 to 14
(S101) and pins 24 to 29 (S102)), select the RS232 format for correct operation of the
external equipment (see the Split-site Remote Control NGT Systems Reference Manual).
The microprocessor IC12 on the Microprocessor & TCVR Interface PCB communicates
to the RS232 microprocessor IC103 via the I
Backplane PCB to the General Purpose Input/Output PCB via connector P1 (pins 8a, 8b,
and 7b) and applied directly to the microprocessor pins 19 (INT IN), 22 (SCL), and 23
(SDA). The interrupt output line from pin 20 (INT OUT) is combined via buffer IC101a
and transistor V102 at P1 pin 7b, resulting in a bidirectional interrupt line at this point.
The operation control logic within the UART IC107 receives operation commands from
the microprocessor and generates appropriate signals to control the device. The
commands include the baud rate, parity selection, data width, and stop bit parameters set
by the 8-bit mode switch S101. The commands permit the UART to communicate with
the microprocessor via the data bus buffer.
Serial data from the external equipment is applied via the option interface cable to input
pin 17 (RxD) of the level translator IC108, and the buffered data (pin 16) is applied to
pin 2 of the UART IC107. The data is converted from serial to parallel, and applied via
the data bus to the microprocessor.
Parallel data from the microprocessor is applied via the data bus to the UART IC107, and
the resulting serial data at pin 3 (TxD) is connected to pin 15 of the level translator
IC108. The output at pin 18 is connected via the interface cable to the external
equipment.
The CTS and RTS control lines connected between the external equipment and the
UART via the translator are part of the enable and handshake mechanism used when
transferring data.
The analog input and output circuits connected to the microprocessor IC103 and the
DSR and DTR lines connected to the level translator are not enabled but are included for
future use if required.
NGT Transceiver System Technical Service Manual
IC105—an EPROM containing control firmware. The microprocessor selects the
EPROM via the PSEN signal (pin 47).
IC106—a RAM device supplementing the microprocessor's internal RAM. It is
selected via the microprocessor's Read or Write signals (pins 30 and 31) in
conjunction with address lines A13 and A15, and is used for chip select.
IC107—UART, a bidirectional serial to parallel data converter.
8571—Technical description
2
C bus, and is connected from the
347