Eurotech Appliances zeus pxa270 Manuel D’Utilisation

 

© 2007 Eurotech Ltd    Issue D 

Supported on Channel C of the external Quad UART, COM3 port can be configured by 

software as RS232 or RS485/RS422. 
The port is buffered to RS232 (or RS485/RS422) levels with ±15kV ESD protection. 

RS232 interface supports full handshaking and modem control signals. The maximum 

baud rate on this channel is 921.6 Kbaud. COM3 RS232 interface is connected to the 

connector J19, and RS485/422 interface is connected to the connector J18. For pin 

assignment and connector details, see 

 on page 

Three control outputs of I

2

C GPIO expander (I

2

C address 0x21) are used to select one 

of the operating modes RS232, RS485 or RS422. The selection is implemented by 

using two control signals (U3_RS232EN, U3_RS422EN) to enable/disable the associated 

transceivers. The control signal combinations are shown in the following table: 

1 X  RS232 
0 

0 

RS485 Full duplex 

0 

1 

RS422 Half duplex 

 

 

U3_RS232EN and U3_RS422EN are at logic ‘1’ upon 

reset. 

The control signal U3_TERM# is used to enable/disable the RS485/422 line 

termination and must be enabled if the ZEUS board is at the end of the network. The 

following table shows the usage of U3_TERM# signal: 

Ω) 

0 Connected 
1 Disconnected 

 

  U3_TERM# is at logic ‘1’ upon reset. 

The RS485/422 driver (LTC2859) on ZEUS features a logic-selectable reduced slew 

mode that softens the driver output edges to control the high frequency EMI emissions 

from equipment and data cables. The reduced slew rate mode is entered by taking the 

SLO# pin low, where the data rate is limited to about 250kbps. Slew limiting also 

mitigates the adverse effects of imperfect transmission line termination caused by 

stubs or mismatched cables. 

U3_RS485_SLO# (EXP2_GPIO 5)  Slew rate 
0 Reduced 
1 Normal