HIP7010P Просмотр технического описания (PDF) - Intersil
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HIP7010P Datasheet PDF : 20 Pages
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HIP7010
The terms short and long are often used to refer to pulses of
duration TV1 and TV2 respectively.
TABLE 1. J1850 TV DEFINITIONS
Table 2 summarizes the complete set of symbol definitions
based on duration and state.
TABLE 2. J1850 SYMBOL DEFINITIONS
TV ID
Illegal
TV1
TV2
TV3
TV4
TV5
TV6
DURATION (ALL TIMES IN µs)
MINIMUM
NOMINAL
MAXIMUM
0
NA
≤ 34
>34
64
≤ 96
>96
128
≤ 163
>163
200
≤ 239
>239
280
NA
>239
300
NA
>280
300
NA
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.
SYNCHRONIZED
0 DATA BIT
0
1 DATA BIT
1
J1850 BUS
0
LONGER ACTIVE
PULSE (0)
CONTROLS THE BUS
FIGURE 4A. DOMINANCE OF ACTIVE 0 DATA BIT
SYNCHRONIZED
SYMBOL
0 Data
1 Data
SOF (Start of Frame)
EOD (End of Data)
EOF (End of Frame)
IFS (Inter-Frame Separation)
IDLE (Idle Bus)
NB (Normalization Bit)
BRK (Break)
DEFINITION
Passive TV1 or Active TV2
Active TV1 or Passive TV2
Active TV3
Passive TV3
Passive TV4
Passive TV6
Passive >TV6 Nominal
ActiveTV1 or Active TV2
Active TV5
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
0 DATA BIT
0
1 DATA BIT
1
J1850 BUS
0
SHORTER PASSIVE
PULSE (0)
CONTROLS THE BUS
FIGURE 4B. DOMINANCE OF PASSIVE 0 DATA BIT
FIGURE 4.
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)
8
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