WinSystems EBC-LP, Operation Manual

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COM2 - RS- 485
Important Note : All serial termination components are surface mount 0805 packages. These
should only be installed by surface mount qualified individuals.
2.10.3
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 EBC-LP 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.
030530 EBC-LP OPERATIONS MANUAL Page 2-11
WinSystems - "The Embedded Authority"
3 2 1
o o o
1 2 3
o o o
U28 - Not In stalled
U29 - In stalled
U30 - Not In stalled
1 o o 6
2 o o 7
3 o o 8
4 o o 9
5 o
J13 J14
COM2 DB9
N/C
TX/RX+
TX/RX-
N/C
GND
N/C
N/C
N/C
N/C
VCC
R29
R31
R32
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.