Eurotech Appliances PXA255 RS422, RS485, COM4 – RS232 interface, COM5

VIPER Technical Manual	Detailed hardware description

COM4 – RS232 interface

Supported on Channel 0 of an external Exar XR16C2850 with 128bytes of Tx and Rx VL FIFOs, and buffered to RS232 levels with ±15kV ESD protection. The maximum baud

rate on this channel is 115.2kb/s. On special request this can be increased to

921.6kb/s. Please contact Eurotech Ltd (see Appendix 61H62H63H367HA – Contacting Eurotech , page

101 368H) for details.

COM5 – RS422/485 interface

Supported on Channel 1 of an external Exar XR16C2850 with 128bytes of Tx and Rx VL FIFOs, and buffered to RS422/485 levels with ±15kV ESD protection, to provide

support for RS422 (default) and RS485 (jumper selectable) interfaces. The maximum baud rate on this channel is 115.2kb/s. On special request this can be increased to

921.6kb/s. Please contact Eurotech Ltd (see Appendix 64H65H66H369HA – Contacting Eurotech , page

101 370H) for details.

RS422

The RS422 interface provides full-duplex communication. The signals available are TXA, TXB, RXA, RXB and Ground. The maximum cable length for an RS422 system is 4000ft (1200m) and supports 1 transmitter and up to 10 receivers.

To enable RS422 operation, LK6 67Hand LK7 should be in position for RS422 full-duplex. LK4 and LK5 should be made if the board is at the end of the network. See RS485/422 68H configuration – LK4, LK5, LK6 and LK7 , page 99 371H, for details.

RS485

This is a half-duplex interface that provides combined TX and RX signals. PL4 pin 5 provides TXB/RXB and pin 6 provides TXA/RXA. A ground connection is also required for this interface. The maximum cable length for this interface is the same as RS422 (4000ft), but RS485 supports up to 32 transmitters and receivers on a single network. Only one transmitter should be switched on at a time.

The VIPER uses the RTS signal to control transmission. When this signal is at logic ‘1’ the driver is switched off and data can be received from other devices. When the RTS line is at logic ‘0’ the driver is on. Any data that is transmitted from the VIPER is automatically echoed back to the receiver. This enables the serial communications software to detect that all data has been sent and disable the transmitter when required. LK6 69Hand LK7 should be in position RS485 half-duplex to enable the RS485

interface. See RS485/422 70Hconfiguration – LK4, LK5, LK6 and LK7 , page 99 372H, for details. The UART used on the VIPER for COM5 has extended features including auto-RTS control for RS485. This forces the RTS signal to change state (and therefore the direction of the RS485 transceivers) when the last bit of a character has been sent onto the wire. Please refer to the XR16C2850 datasheet on the Development Kit CD.

LK4 71Hand LK5 provide parallel line termination resistors and should be made if the VIPER is at the end of the network.

The RS422/485 cable shield MUST be connected between TITAN J1 pin 9 (GND) and the ground connection of the connecting equipment. Failure to do so can result in TITAN RS422/485 transceiver being permanently damaged.