Datasheet

Byte Data Link Controller Module
Transmitting An In-Frame Response (IFR)
MC9S12DP256 — Revision 1.1
Byte Data Link Controller Module
initial portion of the message, and the intended receiver responds by
transmitting the desired data in an IFR. In most cases, the original
message requiring a Type 3 IFR is addressed to one particular node, so
no arbitration should take place during the IFR portion of the message.
BDLC IFR Transmit
Control Bits
The BDLC has three bits which are used to control the transmission of
an In-Frame Response. These bits, all located in DLCBCR2, are TSIFR,
TMIFR1 and TMIFR0. Each is used in conjunction with the TEOD bit to
transmit one of three IFR types defined in SAE J1850. What follows is a
brief description of each bit.
Because each of the bits used for transmitting an IFR with the BDLC is
used to transmit a particular type of IFR, only one bit should be set by
the CPU at a time. However, should more than one of these bits get set
at one time, a priority encoding scheme is used to determine which type
of IFR is sent. This scheme prevents unpredictable operation caused by
conflicting signals to the BDLC. Table 120 illustrates which IFR bit will
actually be acted upon by the BDLC should multiple IFR bits get set at
the same time.
NOTE: As with transmitted messages, IFRs transmitted by the BDLC will also
be received by the BDLC. For a description of how IFR bytes received
by the BDLC should be handled, refer to Receiving An In-Frame
Response (IFR).
Table 120 IFR Control Bit Priority Encoding
Read/Write Actual
TSIFR TMIFR1 TMIFR0 TSIFR TMIFR1 TMIFR0
000000
1XX100
01X010
001001
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