HIP7010 datasheet(8/20 Pages) INTERSIL

8 / 20 page

The terms

short and long are often used to refer to pulses of

duration TV1 and TV2 respectively.

VPW is a non-return-to-zero (NRZ) protocol in which each

transition represents a complete bit of information. Accord-

ingly, a

0 data bit will sometimes be transmitted as a passive

pulse and sometimes as an active pulse. Similarly, a

1 data

bit will sometimes be transmitted as a passive pulse and

sometimes as an active pulse. In order to accommodate

arbitration (see Bus Arbitration) a

long active pulse repre-

sents a 0 data bit and a

short active pulse represents a 1

data bit. Complementing this fact, a

short passive pulse rep-

resents a 0 and a

long passive pulse represents a 1. Starting

from a transition to the active state, a 0 data bit will maintain

the active level longer than a 1. Similarly, starting from a

transition to the passive state, a 0 data bit will return to the

active level quicker than a 1. These facts give rise to the

dominance of 0’s over 1’s on the J1850 bus as depicted in

Figure 4. See Bus Arbitration for additional details.

Table 2 summarizes the complete set of symbol deﬁnitions

based on duration and state.

In Frame Response (IFR)

The distinction between two of the passive symbols, EOD and

EOF, is subtle but important (refer to Figure 5). The EOD (TV3)

interval signiﬁes that the originator of the message is done

broadcasting and any nodes which have been requested to

respond (i.e., to acknowledge receipt of the message) can now

do so. The EOD interval begins when the transmitting node has

completed sending the eighth bit of the check byte. The trans-

mitter simply releases the bus and allows it to revert to a pas-

sive state. In the course of normal messaging, no node can

seize the bus until an EOD time has been detected. Once an

EOD has elapsed, any nodes which are scheduled to produce

an IFR will arbitrate for control of the bus (see Bus Arbitration)

and respond appropriately. If no responses are forthcoming the

bus remains in the passive state until an EOF (TV4) interval

has elapsed. After the EOF has been generated, the frame is

considered closed and the next communications on the bus will

represent a totally new message.

IFRs can consist of multiple bytes from a single respondent,

one byte from a single respondent, or one byte from multiple

respondents. In all cases the ﬁrst response byte must be pre-

ceded by a

normalization bit (NB) which serves as a start of

response symbol and places the bus in an active state so that

following the IFR byte(s) the bus will be left in the passive state.

The NB symbol is by deﬁnition active, but can be either TV1

or TV2 in duration. The long variety (TV2) signiﬁes the IFR

contains a CRC byte. The short variety (TV1) precedes an

IFR without CRC.

Message Types

Messages are classiﬁed into one of four

Types according to

whether the message has an IFR and what kind of IFR it is.

The deﬁnitions are:

• Type 0 - No IFR

• Type 1 - One byte IFR from a single respondent

(no CRC byte)

• Type 2 - One byte IFRs from multiple respondents

(no CRC byte)

• Type 3 - Multiple byte IFR from a single respondent

(CRC appended)

TABLE 1. J1850 TV DEFINITIONS

TV ID

DURATION (ALL TIMES IN

µs)

MINIMUM

NOMINAL

MAXIMUM

Illegal

≤34

TV1

>34

≤96

TV2

>96

128

≤163

TV3

>163

200

≤239

TV4

>239

280

TV5

>239

300

TV6

>280

300

BIT

DATA

BIT

DATA

BUS

J1850

SYNCHRONIZED

PULSE (0)

LONGER ACTIVE

CONTROLS THE BUS

FIGURE 4A. DOMINANCE OF ACTIVE 0 DATA BIT

BIT

DATA

BIT

DATA

BUS

J1850

SYNCHRONIZED

PULSE (0)

SHORTER PASSIVE

CONTROLS THE BUS

FIGURE 4B. DOMINANCE OF PASSIVE 0 DATA BIT

FIGURE 4.

TABLE 2. J1850 SYMBOL DEFINITIONS

SYMBOL

DEFINITION

0 Data

Passive TV1 or Active TV2

1 Data

Active TV1 or Passive TV2

SOF (Start of Frame)

Active TV3

EOD (End of Data)

Passive TV3

EOF (End of Frame)

Passive TV4

IFS (Inter-Frame Separation)

Passive TV6

IDLE (Idle Bus)

Passive >TV6 Nominal

NB (Normalization Bit)

ActiveTV1 or Active TV2

BRK (Break)

Active TV5

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