J1850 Byte Level Protocol Decoder (JBLPD)
J1850 BYTE LEVEL PROTOCOL DECODER (Cont’d)
10.9.7.1 Un-Stacked Registers
next frame will not be cancelled for these errors,
so TRDY would not get set.
STATUS REGISTER (STATUS)
R240 - Read/Write
Register Page: 23
Reset Value: 0100 0000 (40h)
– An RBRK error condition cancels all transmits for
this frame or any successive frames, so the
TRDY bit will always be immediately set on an
RBRK condition.
7
0
TRDY is set on reset or while CONTROL.JE is re-
set, or while the CONTROL.JDIS bit is set.
If the TRDY_M bit of the IMR register is set, when
this bit is set an interrupt request occurs.
0: TXOP register not ready to receive a new op-
code
ERR TRDY RDRF TLA
RDT EODM EOFM IDLE
The bits of this register indicate the status of the
JBLPD peripheral.
This register is forced to its reset value after the
MCU reset and while the CONTROL.JDIS bit is
set. While the CONTROL.JE bit is reset, all bits ex-
cept IDLE are forced to their reset values.
1: TXOP register ready to receive a new opcode
Bit 5 = RDRF Receive Data Register Full Flag.
RDRF is set when a complete data byte has been
received and transferred from the serial shift regis-
ter to the RXDATA register.
RDRF is cleared when the RXDATA register is
read (by software or by DMA). RDRF is also
cleared on reset or while CONTROL.JE is reset, or
while CONTROL.JDIS bit is set.
If the RDRF_M bit of the IMR register is set, when
this bit is set an interrupt request occurs.
0: RXDATA register doesn’t contain a new data
1: RXDATA register contains a new data
Bit 7 = ERR Error Flag.
The ERR bit indicates that one or more bits in the
ERROR register have been set. As long as any bit
in the ERROR register remains set, the ERR bit re-
mains set. When all the bits in the ERROR register
are cleared, then the ERR bit is reset by hardware.
The ERR bit is also cleared on reset or while the
CONTROL.JE bit is reset, or while the CON-
TROL.JDIS bit is set.
If the ERR_M bit of the IMR register is set, when
this bit is set an interrupt request occurs.
0: No error
Bit 4 = TLA Transmitter Lost Arbitration.
1: One or more errors have occurred
The TLA bit gets set when the transmitter loses ar-
bitration while transmitting messages or type 1
and 3 IFRs. Lost arbitration for a type 2 IFR does
not set the TLA bit. (Type 2 messages require re-
tries of the physical address if the arbitration is lost
until the frame length is reached (if NFL=0)). The
TLA bit gets set when, while transmitting a MSG,
MSG+CRC, IFR1, IFR3, or IFR3+CRC, the decod-
ed VPWI data bit symbol received does not match
the VPWO data bit symbol that the JBLPD is at-
tempting to send out. If arbitration is lost, the
VPWO line is switched to its passive state and
nothing further is transmitted until an end-of-data
(EOD) symbol is detected on the VPWI line. Also,
any queued transmit opcode scheduled for trans-
mission during this frame is cancelled (but the
TRA bit is not set).
Bit 6 = TRDY Transmit Ready Flag.
The TRDY bit indicates that the TXOP register is
ready to accept another opcode for transmission.
The TRDY bit is set when the TXOP register is
empty and it is cleared whenever the TXOP regis-
ter is written (by software or by DMA). TRDY will
be set again when the transmit state machine ac-
cepts the opcode for transmission.
When attempting to transmit a data byte without
using DMA, two writes are required: first a write to
TXDATA, then a write to the TXOP.
– If a byte is written into the TXOP which results in
TRA getting set, then the TRDY bit will immedi-
ately be set.
The TLA bit can be cleared by software writing a
logic “zero” in the TLA position. TLA is also cleared
on reset or while CONTROL.JE is reset, or while
CONTROL.JDIS bit is set.
If the TLA_M bit of the IMR register is set, when
this bit is set an interrupt request occurs.
– If a TLA occurs and the opcode for which TRDY
is low is scheduled for this frame, then TRDY
will go high, if the opcode is scheduled for the
next frame, then TRDY will stay low.
– If an IBD, IFD or CRCE error condition occurs,
then TRDY will be set and any queued transmit
opcode scheduled to transmit in the present
frame will be cancelled by the JBLPD peripher-
al. A MSGx opcode scheduled to be sent in the
0: The JBLPD doesn’t lose arbitration
1: The JBLPD loses arbitration
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STMICROELECTRONICS [ ST ]
