Article

RS232-to-RS485 Half-Duplex Adapter

advantages of balanced lines

This project has been designed to interface an EIA-232 channel to an EIA-485 half-duplex bus. We should do so because EIA-485 offers more features than 232, especially where we apply a long distance wired communication involving more than two devices.The EIA-232 standard, formerly known as RS-232, was introduced about thirty years ago, well before the first application of desktop sized personal computers. The RS-232 standard mainly covers the communication between DTEs and DCEs, where DTEs are Data Circuit Terminating Equipments, and DCEs are Data Communication Equipments. A typical DTE could be just a video terminal, a printer, or even a personal computer — it can operate either as a source or destination of data, hence it is the equipment where the communication is terminated.

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Materials

020003-PCB.pdf

020003-11.zip

Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

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The use of our Gerber files is provided under a modified Creative Commons license. Creative Commons offers authors, scientists, educators and other creatives the freedom to handle their copyright in a more free way without losing their ownership.

PCB

Download Gerber file: 020003-1.zip

Component list

Resistors:
R1,R2,R3 = 1kOhm
R4 = 10kOhm 8-way or 6-way SIL array
R5,R6 = 100Ohm
R7,R8,R9 = 10kOhm
R10 = 120Ohm
R11,R13 = 680Ohm
R12 = 100Ohm
Capacitors:
C1,C2 = 22pF
C3-C6 = 1µ F 16V radial
C7 = 22µ F 16V radial
C8,C9,C11,C12,C13 = 100nF
C10 = 10µ F 16V radial
Semiconductors:
D1,D2,D3 = LED, red, low current
IC1 = PIC16C54-HS/P, programmed, order code 020003-41
IC2 = MAX232CP
IC3 = 74HCT00
IC4 = 75176BP
IC5 = 7805
B1 = bridge rectifier B40C800, round case (40V piv, 800mA)
Miscellaneous:
JP1,JP2,JP3 = jumper
K1 = 9-way sub-D socket (female), angled pins, PCB mount
K2 = mains adaptor socket, PCB mount
K3 = 3-way PCB terminal block, lead pitch 5mm
S1 = 6-way DIP-switch
X1 = 4MHz quartz crystal