8-19

J1850 COMMUNICATIONS CONTROLLER

8.6.3 Programming the J1850 Delay Compensation (J_DLY) RegisterThe J1850 delay compensation register (Figure 8-18) allows you to program the necessary delaytime through the external transceiver to compensate for the inherent propagation delays and toaccurately resolve bus contention during arbitration.
2 Reserved; for compatibility with future devices, write zero to this bit.
1:0 PRE1:0 J1850 Oscillator Prescaler
These bits ensure proper operation of the J1850 peripheral at the supported
input frequencies (FXTAL1).
PRE1 PRE0 FXTAL1
00 8 MHz
0 1 12 MHz
1 0 16 MHz
1 1 20 MHz
J_CFG Address:
Reset State: 1F54H
00H
The J1850 configuration (J_CFG) register selects the proper oscilator prescaler, initiates transmission
break for debug, invokes clock quadrupling operation, and selects the normalizartion bit format. This
byte register can be directly addressed through
windowing
. All J1850 bus activity is ignored until you
first write to this register.
7 0
NBF IFR3 4XM TXBRK RXPOL PRE1 PRE0
Bit
Number Bit
Mnemonic Function

Figure 8-17. J1850 Configuration (J_CFG) Register (Continued)