MC908AS60ACFU Datasheet, PDF (357/414 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

BDLC CPU Interface
the off-chip analog transceiver is no longer in loopback mode, the BDLC waits for an EOF symbol
before attempting to transmit.
1 = Input to the analog physical interface’s final drive stage is looped back to the BDLC receiver.
The J1850 bus is not driven.
0 = The J1850 bus will be driven by the BDLC. After the bit is cleared, the BDLC requires the bus
to be idle for a minimum of end-of-frame symbol time (t_TRV4) before message reception or a
minimum of inter-frame symbol time (t_TRV6) before message transmission. (See 28.1.15 BDLC
Transmitter VPW Symbol Timings.
DLOOP — Digital Loopback Mode Bit
This bit determines the source to which the digital receive input (BDRxD) is connected and can be used
to isolate bus fault conditions (see Figure 27-13). If a fault condition has been detected on the bus, this
control bit allows the programmer to connect the digital transmit output to the digital receive input. In
this configuration, data sent from the transmit buffer will be reflected back into the receive buffer. If no
faults exist in the BDLC, the fault is in the physical interface block or elsewhere on the J1850 bus.
1 = When set, BDRxD is connected to BDTxD. The BDLC is now in digital loopback mode.
0 = When cleared, BDTxD is not connected to BDRxD. The BDLC is taken out of digital loopback
mode and can now drive the J1850 bus normally.
RX4XE — Receive 4X Enable Bit
This bit determines if the BDLC operates at normal transmit and receive speed (10.4 kbps) or receive
only at 41.6 kbps. This feature is useful for fast download of data into a J1850 node for diagnostic or
factory programming of the node.
1 = When set, the BDLC is put in 4X receive-only operation.
0 = When cleared, the BDLC transmits and receives at 10.4 kbps.
NBFS — Normalization Bit Format Select Bit
This bit controls the format of the normalization bit (NB). (See Figure 27-18.) SAE J1850 strongly
encourages using an active long (logic 0) for in-frame responses containing cyclical redundancy check
(CRC) and an active short (logic 1) for in-frame responses without CRC.
1 = NB that is received or transmitted is a 0 when the response part of an in-frame response (IFR)
ends with a CRC byte. NB that is received or transmitted is a 1 when the response part of an
in-frame response (IFR) does not end with a CRC byte.
0 = NB that is received or transmitted is a 1 when the response part of an in-frame response (IFR)
ends with a CRC byte. NB that is received or transmitted is a 0 when the response part of an
in-frame response (IFR) does not end with a CRC byte.
TEOD — Transmit End of Data Bit
This bit is set by the programmer to indicate the end of a message is being sent by the BDLC. It will
append an 8-bit CRC after completing transmission of the current byte. This bit also is used to end an
in-frame response (IFR). If the transmit shadow register is full when TEOD is set, the CRC byte will be
transmitted after the current byte in the Tx shift register and the byte in the Tx shadow register have
been transmitted. (See 27.5.3 Rx and Tx Shadow Registers for a description of the transmit shadow
register.) Once TEOD is set, the transmit data register empty flag (TDRE) in the BDLC state vector
register (BSVR) is cleared to allow lower priority interrupts to occur. (See 27.6.4 BDLC State Vector
Register.)
1 = Transmit end-of-data (EOD) symbol
0 = The TEOD bit will be cleared automatically at the rising edge of the first CRC bit that is sent or
if an error is detected. When TEOD is used to end an IFR transmission, TEOD is cleared when
the BDLC receives back a valid EOD symbol or an error condition occurs.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
Freescale Semiconductor
357