275h, 276h – Eurotech Appliances VIPER / VIPER-LITE PXA255 User Manual
Page 65
VIPER Technical Manual
Detailed hardware description
© 2007 Eurotech Ltd Issue E
65
COM4 – RS232 interface
Supported on Channel 0 of an external Exar XR16C2850 with 128bytes of Tx and Rx
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 A – Contacting Eurotech
, page
) for details.
COM5 – RS422/485 interface
Supported on Channel 1 of an external Exar XR16C2850 with 128bytes of Tx and Rx
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 A – Contacting Eurotech
, page
) 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,
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
configuration – LK4, LK5, LK6 and LK7
, 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.
should be in position RS485 half-duplex to enable the RS485
interface. See
RS485/422 configuration – LK4, LK5, LK6 and LK7
, 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.
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.
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