ST92F124 datasheet(297/429 Pages) STMICROELECTRONICS

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J1850 Byte Level Protocol Decoder (JBLPD)

J1850 BYTE LEVEL PROTOCOL DECODER (Cont’d)

10.9.4 Peripheral Functional Modes

The JBLPD can be programmed in 3 modes, de-

pending on the value of the JE and JDIS bits in the

CONTROL register, as shown in Table 55.

Table 55. JBLPD functional modes

Depending on the mode selected, the JBLPD is

able or unable to transmit or receive messages.

Moreover the power consumption of the peripheral

is affected.

Note: The configuration with both JE and JDIS set

is forbidden.

10.9.4.1 JBLPD Enabled

When the JBLPD is enabled (CONTROL.JE=1), it

is able to transmit and receive messages. Every

feature is available and every register can be writ-

ten.

10.9.4.2 JBLPD Suspended (Low Power Mode)

When the JBLPD is suspended (CONTROL.JE=0

and CONTROL.JDIS=0), all the logic of the

JBLPD is stopped except the decoder logic.

This feature allows a reduction of power consump-

tion when the JBLPD is not used, even if the de-

coder is able to follow the bus traffic. So, at any

time the JBLPD is enabled, it is immediately syn-

chronized with the J1850 bus.

Note: While the JBLPD is suspended, the STA-

TUS register, the ERROR register and the SLP bit

of the PRLR register are forced into their reset val-

ue.

10.9.4.3 JBLPD Disabled (Very Low Power

Mode)

Setting the JDIS bit in the CONTROL register, the

JBLPD is stopped until the bit is reset by software.

Also the J1850 decoder is stopped, so the JBLPD

is no longer synchronized with the bus. When the

bit is reset, the JBLPD will wait for a new idle state

on the J1850 bus. This mode can be used to mini-

mize power consumption when the JBLPD is not

used.

Note: While the JDIS bit is set, the STATUS regis-

ter, the ERROR register, the IMR register and the

SLP, TEOBP and REOBP bits of the PRLR regis-

ter are forced to their reset value.

Note: In order that the JDIS bit is able to reset the

IMR register and the TEOBP and REOBP bits, the

JDIS bit must be left at 1 at least for 6 MCU clock

cycles (3 NOPs).

Note: The JE bit of CONTROL register cannot be

set with the same instruction that reset the JDIS

bit. It can be set only after the JDIS bit is reset.

JDIS

mode

JBLPD Disabled

JBLPD Suspended

JBLPD Enabled

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