ST92F124 datasheet(316/429 Pages) STMICROELECTRONICS

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J1850 Byte Level Protocol Decoder (JBLPD)

J1850 BYTE LEVEL PROTOCOL DECODER (Cont’d)

Bit 0 = IBD Invalid Bit Detect.

The IBD bit gets set whenever the receiver detects

that the filtered VPWI pin was not fixed in a state

long enough to reach the minimum valid symbol

time of Tv1 (or 35 µs). Any timing event less than

35 µs (and, of course, > 7 µs since the VPWI digit-

al filter will not allow pulses less than this through

its filter) is considered as noise and sets the IBD

accordingly. At this point the JBLPD peripheral will

cease transmitting and receiving any information

until a valid EOF symbol is received.

IBD errors are inhibited if the JBLPD peripheral is

in the “sleep or filter and NOT presently transmit-

ting” mode. An IBD error occurs once for a frame.

Afterwards, the receiver is disabled until an EOFM

symbol is received, and queued transmits for the

present frame are cancelled (but the TRA bit is not

set).

IBD is cleared when ERROR is read. Note that if

an invalid bit is detected during a bus idle condi-

tion, the IBD flag gets set and a new EOFmin must

be seen after the invalid bit before commencing to

receive again. IBD is also cleared while the CON-

TROL.JE bit is reset or while the CONTROL.JDIS

bit is set and on reset.

0: No invalid bit detected

1: Invalid bit detected

JBLPD INTERRUPT VECTOR REGISTER (IVR)

R248- Read/Write (except bits 2:1)

Reset Value: xxxx xxx0 (xxh)

Bit 7:3 = V[7:3] Interrupt Vector Base Address.

User programmable interrupt vector bits.

Bit 2:1 = EV[2:1] Encoded Interrupt Source (Read

Only).

EV2 and EV1 are set by hardware according to the

interrupt source, given in Table 59 (refer to the

Status register bits description about the explana-

tion of the meaning of the interrupt sources)

Table 59. Interrupt Sources

Bit 0 = Reserved.

JBLPD PRIORITY LEVEL REGISTER (PRLR)

R249- Read/Write

Reset Value: 0001 0000 (10h)

Bit 7:5 = PRL[2:0] Priority level bits

The priority with respect to the other peripherals

and the CPU is encoded with these three bits. The

value of “0” has the highest priority, the value “7”

has no priority. After the setting of this priority lev-

el, the priorities between the different Interrupt

sources and DMA of the JBLPD peripheral is hard-

ware defined (refer to the “Status register” bits de-

scription, the “Interrupts Management” and the

section about the explanation of the meaning of

the interrupt sources).

Depending

the

value

the

OP-

TIONS.DMASUSP bit, the DMA transfers can or

cannot be suspended by an ERROR or TLA event.

Refer to the description of DMASUSP bit.

Table 60. Internal Interrupt and DMA Priorities

without DMA suspend mode

Table 61. Internal Interrupt and DMA Priorities

with DMA suspend mode

EV2

EV1

EV2

EV1

Interrupt Sources

ERROR, TLA

EODM, EOFM

RDRF, REOB

TRDY, TEOB

PRL2

PRL1

PRL0

SLP

REOBP TEOBP

Priority Level

Event Sources

Higher Priority

TX-DMA

RX-DMA

ERROR, TLA

EODM, EOFM

RDRF, REOB

Lower Priority

TRDY, TEOB

Priority Level

Event Sources

Higher Priority

ERROR, TLA

TX-DMA

RX-DMA

EODM, EOFM

RDRF, REOB

Lower Priority

TRDY, TEOB

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