参数资料
型号: ST72511R6T1/XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PQFP64
封装: 14 X 14 MM, TQFP-64
文件页数: 14/164页
文件大小: 1043K
代理商: ST72511R6T1/XXX
ST72311R, ST72511R, ST72512R, ST72532R
110/164
CONTROLLER AREA NETWORK (Cont’d)
10.7.3.4 Bit Timing Logic
The bit timing logic monitors the serial bus-line and
performs sampling and adjustment of the sample
point by synchronizing on the start-bit edge and re-
synchronizing on following edges.
Its operation may be explained simply when the
nominal bit time is divided into three segments as
follows:
– Synchronisation segment (SYNC_SEG): a bit
change is expected to lie within this time seg-
ment. It has a fixed length of one time quanta (1
xtCAN).
– Bit segment 1 (BS1): defines the location of the
sample point. It includes the PROP_SEG and
PHASE_SEG1 of the CAN standard. Its duration
is programmable between 1 and 16 time quanta
but may be automatically lengthened to compen-
sate for positive phase drifts due to differences in
the frequency of the various nodes of the net-
work.
– Bit segment 2 (BS2): defines the location of the
transmit point. It represents the PHASE_SEG2
of the CAN standard. Its duration is programma-
ble between 1 and 8 time quanta but may also be
automatically shortened to compensate for neg-
ative phase drifts.
The resynchronization jump width (RJW) defines
an upper bound to the amount of lengthening or
shortening of the bit segments. It is programmable
between 1 and 4 time quanta.
A valid edge is defined as the first transition in a bit
time from dominant to recessive bus level provid-
ed the controller itself does not send a recessive
bit.
If a valid edge is detected in BS1 instead of
SYNC_SEG, BS1 is extended by up to RJW so
that the sample point is delayed.
Conversely, if a valid edge is detected in BS2 in-
stead of SYNC_SEG, BS2 is shortened by up to
RJW so that the transmit point is moved earlier.
As a safeguard against programming errors, the
configuration of the Bit Timing Register (BTR) is
only possible while the device is in STANDBY
mode.
Figure 59. Bit Timing
SYNC_SEG
BIT SEGMENT 1 (BS1)
BIT SEGMENT 2 (BS2)
NOMINAL BIT TIME
1x tCAN
tBS1
tBS2
SAMPLE POINT
TRANS MIT POINT
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