Serial RS232 to RS485 Interface Converter

I. Summary
In order to carry through remote data communication between computer and peripheral equipment or intelligent instrument with various standards of serial interfaces, it must make interconversion between standard serial interfaces. Compatible RS-232C/RS-485 standards, it is able to convert mono-end RS-232 signal to balance difference RS-485 signal and extend the communication distance to 1.2km. No external power but adopts a particular RS-232 charge pump to drive the system, and gains electricity without initializing the RS-232 series interface. An internal zero delay auto transceiver and particular I/O circuit automatically control the data Stream direction instead of any handshake signal (for example RTS, DTR etc. ). There by in guarantees the function under RS-485 without changing the program compiled under RS-232 half-duplex mode and assures the adaptation to current operation software and interface hardware. The transmission rateof300-115.2kbps. Is capable of applying between host computers, host computer and is extensions or external equipment and forms dot to dot, dot to dots remote and multi-communication network, It implements multi-machine response communication and commonly used in industry automation control system, all-one-card, access control system, consumption system, time and attendance system, parking system, self-service banking system, bus charging system, highway toll station system and so on.

II. Capabilities parameter
1. Interface feature: RS-232C RS-485 standard interface compatible with EIA TIA
2. Electric interface: RS-232 end DB9 female connector RS-485 end DB9 male connector
3. Working mode: Asynchronism half-duplex difference transmission
4. Transmission media: Twisted -pair or STP
5. Transmission rate: 300-115.2KBPS
6. External discharge dimension: 63mmX33mmX17mm
7. Working circumstance: - 25 to 70 degree, relative humidity 5%to95%
8. Transmission distance: 1, 200m(RS-485 end) 5m(RS-232 end)

III. Connector an signal:
RS-232C pin distribution
DB9 Female (PIN) RS-232C Interface Signal
1 Protective
2 RXD SIN
3 TXD SOUT
4 DTR
5 GND
6 DSR
7 RTS
8 CTS
9 RI
RS-485 data output & connector and pin distribution
DB9 Male (PIN) Data Output RS-485 Half Duplex
1 T/R+ RS-485(A+)
2 T/R- RS-485(B-)
3 RXD+ N/C
4 RXD- N/C
5 GND Ground wire
6 VCC +5V standby power input

IV. Hardware installation & application
1. The product appearance adopts DB9M/DB9F general transit plugs, output plug carries ordinary terminal, you can use UTP or shielded wire, easy connection and disassembly.
2. T/R+, T/R- stands for receiving/sending A+ B-, VCC stands for standby power input, GND stands for public ground wire
3. Point-to-point or point-to-multipoint half-duplex communication, connect 2 wires (T/R+ T/R-), connection principle is "T/R+" connects to opposite "T/R+", "T/R-" connects to opposite "T/R-"; RS-485 half-duplex mode, connect "T/R+" to opposite "A+", "T/R-" to opposite "B-". (Remark: A+ for(485+), B-for (485-))

HC-01 interface supports 2 communication modes as below:
1. Point-to-point 2 wires half-duplex
2. point-to-multipoint 2 wires half-duplex
When converter works under half-duplex connection, it needs to install a matching resistance (data 120 ohm1/4W) for preventing signal reflection and interference.

V. Communication sketch map
RS-232 to RS-485 conversion
1. RS-485 Point-to-point 2 wires half-duplex

2. RS-485 point-to-multipoint 2 wires half-duplex

3. HC-01 half-duplex communication connect between interface converter


VI. Problem and resolution
1. Data communication failure
A. Check if RS-232 interface connection is correct
B. Check if RS-232 output connection is correct
C. Check if connection ends are well connected data loss or mistake
2. Data loss or mistake
A. Check if data rate and format is consistent on both communication ends