2.6
RS-485 Mode Configuration
The RS- 485 multi- drop in ter face is sup ported on both se rial chan nels with the in stal la -
tion of the op tional “Chip Kit”, Win Sys tems part number CK- 75176-2. A sin gle kit is suf fi -
cient to con fig ure both chan nels for RS- 485. RS- 485 is a 2 wire multi- drop in ter face where
only one sta tion at a time talks (trans mits) while all oth ers lis ten (re ceive). RS- 485 usu ally
re quires that the line- pair be ter mi nated at each end of the run. The re quired ter mi na tion
show the cor rect jump er ing, driver IC in stal la tion, DB9 I/O con nec tor pin- out, and ter mi -
na tion re sis tor lo ca tions for each of the chan nels when used in the RS- 485 mode.
2.6.1
Channel 1 - RS-485
981117
PCM-DSPIO/J1708 OPERATIONS MANUAL
Page 2-5
WinSystems - "The Embedded Systems Authority"
U2 - Not Installed
U5 - Installed
U6 - Not Installed
1 o o 6
2 o o 7
3 o o 8
4 o o 9
5 o
J5
J6
CH1 DB9
Jumper Positions
Driver IC Status
I/O Connector Pin Defs
N/C
TX/RX+
TX/RX-
N/C
GND
TX/RX+
TX/RX-
N/C
N/C
1 o
2 o
3 o
1 o
2 o
3 o
RS- 485 NOTE : Be cause RS- 485 uses
a sin gle twisted- pair, all trans mit ters are
con nected in par al lel. Only one sta tion
may trans mit, or have its trans mit ter en -
abled at a time. The trans mit ter En -
able/Dis able is con trolled by Bit 1 in the
Mo dem Con trol reg is ter (RTS). When set,
the trans mit ter is en abled, when cleared
(the nor mal state) the trans mit ter is dis -
abled and the re ceiver is en abled. Note
that it is nec es sary to al low some mini mal
set tling time af ter ena bling the trans mit -
ter bef ore trans mit ting the first char ac -
ter. Like wise, fol low ing a trans mis sion, it
is nec es sary to be sure that all char ac ters
have been com pletely shifted out of the
UART (Check bit 6 in the Line status reg -
is ter) bef ore dis abling the trans mit ter to
avoid chop ping off the last char ac ter.
R15
R16
R17
TX/RX+
TX/RX-
vcc
