Vi-2-10. Rs-232C Interface Circuit - Canon A-200 series Service Manual

VI-2-10. RS-232C Interface Circuit
This circuit consists of the transmitter U50, receivers U43 and U55 and the UART (8250), the
heart of this circuit.
U50 converts TIL compatible signals from the UART to -.12V to
+
12V signals conforming
to the EIA standard, and output them.
U43 and U55 convert EIA level reception signal to TIL level, and send them to the UART.
The functional configuration of the UART is programmed by the software via the data bus.
The UART performs serial-to-parallel conversion on data characters received from a peripheral
device or a MODEM, and parallel-to-serial conversion on data characters received from the CPU.
The CPU can read the complete status of the UART at any time during the functional operation.
Status information reported includes the type and condition of the transfer operations being per­
formed by the UART, as well as any error conditions (parity, overrun, framing, or break interrupt).
The UART includes a programmable baud generator. Also included in the UART is a complete
MODEM control capability, and a processor-interrupt system that minimize the computing time
required to handle the communications link.
The interrupt signal is sent to IR4 terminal of the PIC through the bit4 or the DIP switch S2.
Vee
UART
Xl
SOUT
50 TXD
f74
R18
X2 RTS
DTR
50
50
RTS
DTR
BCLK
RCLK SIN RXD
S2
Blr t: _,
~_f/I~
CTS CTS
~
INT DSR
DSR
123
RSLD
DCD
D7 AI
RI
D6
8250
D5
Vee
Vee
D4
CSl
D3
CSO
D2 DOSTR
Dl DISTR
DO
ADS
IOR-N RD
GND
IOW-N
WR
UART CS MR
RESET
A2, BA2
A2
Al, BAl
Al
AO,BAO AO
Figure 6-18
68