COM2 - RS- 485
2.9.3
SAE J1708 Con figu ra tion
The So ci ety of Auto mo tive En gi neers (SAE) J1708 in ter face is a varia tion of the RS- 485 in ter face
which is used for “Se rial Data Com mu ni ca tions be tween Mi cro com puter Sys tems in Heavy Duty Ve hi -
cle Ap pli ca tions”. It is be yond the scope of this docu ment to go into de tail on the J1708 speci fi ca tion.
The LBC- Plus may be user con fig ured for J1708 by the ad di tion of the CK- 75176-2 “Chip Kit”. One
“Chip Kit” is suf fi cient to con fig ure both chan nels for J1708. The il lus tra tions that fol low show the cor
-
rect jump er ing, driver IC in stal la tion, I/O con nec tor pin defi ni tions, and the ter mi na tion net work de tails
for each of the chan nels when used in J1708 mode.
991206
OPERATIONS MANUAL LBC-Plus
Page 2 - 11
WinSystems - "The Embedded Systems Authority"
1 2 3
o o o
1 2 3
o o o
U5 - Not In stalled
U6 - In stalled
U9 - Not In stalled
1 o o 6
2 o o 7
3 o o 8
4 o o 9
5 o
J9
J11
COM2 DB9
N/C
TX/RX+
TX/RX-
N/C
GND
N/C
N/C
N/C
N/C
VCC
R14
R15
R16
TX/RX+
TX/RX-
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 at a time may trans mit or have
its trans mit ter en abled. The trans mit ter En able/Dis -
able is con trolled in soft ware us ing bit 1 in the Mo -
dem Con trol Reg is ter (RTS). When RTS is set, the
trans mit ter is en abled, and 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.
