User manual

LPC4357 Developer’s Kit - User’s Guide

Page 29

4.17 SP9: RS422/485 Interface

There is a RS422/485 interface on the board. RS422 has individual transmit and receive pairs, while

RS485 share the same signal pair (and is hence half-duplex). By inserting both jumpers in JP9, the two

signal pairs are connected and a RS485 interface is created. By removing the jumpers in JP9 a RS422

interface is created. Via JP10 it is also possible to add termination resistors, if needed.

Direction is controlled via signal GPIO43 and is by default half-duplex (i.e., no simultaneous transmit

and receive). A high level enables the transmitter while a low level enables the receiver. It is possible

to remove R135 and R136 and control the transmitter and receiver individually via JP7 and JP8.

The interface component used (SN65HVD35) has built-in ESD protection.

See picture below for locating relevant components. The table below lists signal connections.

Figure 18 – RS422/484 Interface

Signals

LPC4357

GPIO25_RXD

P2_4 via multiplexor, USART#3 is used

GPIO24_TXD

P9_3 via multiplexor, USART#3 is used

GPIO43

PF_6

RS422/485 part of Connector

J16

From top (pos 1)-to-bottom:

GND

TX-

TX+

RX-

RX+

RS422/485 Select

JP9

Termination Resistors Control

JP10

Transmit Control

JP7

Receive Control

JP8