6
. RS232 SERIAL PORT COMMUNICATION
11
When the communication distance is less than15M, the two sides can communicate directly
connected, and just by using the three lines(transmit line, the receiving line, and the signal ground)
can achieve full-duplex a synchronous serial communication.
When there is no Modem, the maximum communication distance is calculated as follows
RS-232C standard says: When the error rate is of 4%, the required wire capacitance value should be
less than 2500PF. For ordinary Wire, the capacitance value is about 170PF / M.
Allowed distance L = 2500PF / (170PF / M) = 14.7M. calculating this distance, is a conservative. In the
practical applications, when using 9600bps and ordinary shielded twisted pair cable, the distance
can be up to 30 to 35 meters.
The following figure is the easiest way to connect MODEM zero (that is, three-wire connection), And
the 2nd line 3rd line is cross-connect in the figure, because even when direct way to communicate
both look as data terminal equipment, can also be sent to both parties and received from the other.
In this way, either party of the communication can start sending and receiving , as long as there is a
valid request to send RTS efficiently and DTR data terminal is well ready.
Minimalist zero Modem connection of (3-wire)
6.2 Communication protocol Settings
communication Settings: 8 bits 1 stop bit, no check
6.1
. NFC(Near Field Communication)
6.2.1 PC protocol format will be issued on a single chip digital amplifier host state:
Start byte
Instruction type byte
Instruction type
Checksum byte
0xAA
0x05
0x01/Abnormal
0x2E/Abnormal
0x02/Normal
0x2D/Normal
0x03/standby power
0x2C/standby power
0x04/no shaking signal
0x2B/no shaking signal
RXD
TXD
GND
TXD
RXD
RTS
T-4D500R
PC
CTS
DSR
SG
DCD
DTR
RI
1
DCD
2
RxD
3
TxD
4
DTR
5
SG
6
DSR
7
RTS
8
CTS
9
RI
DB-9
RX TX GND
1
2
3
