The Time Quanta (TQ
參數(shù)資料
型號(hào): MCP2510T-E/SO
廠商: Microchip Technology
文件頁(yè)數(shù): 30/80頁(yè)
文件大?。?/td> 0K
描述: IC CAN CONTROLLER W/SPI 18-SOIC
標(biāo)準(zhǔn)包裝: 1,100
控制器類型: CAN 接口
接口: SPI
電源電壓: 4.5 V ~ 5.5 V
電流 - 電源: 10mA
工作溫度: -40°C ~ 125°C
安裝類型: 表面貼裝
封裝/外殼: 18-SOIC(0.295",7.50mm 寬)
供應(yīng)商設(shè)備封裝: 18-SOIC
包裝: 帶卷 (TR)
配用: DV251001-ND - KIT DEVELOPMENT CAN MCP2510
MCP2510
DS21291F-page 36
2007 Microchip Technology Inc.
5.1
Time Quanta
The Time Quanta (TQ) is a fixed unit of time derived
from the oscillator period. There is a programmable
baud-rate prescaler, with integral values ranging from 1
to 64, in addition to a fixed divide by two for clock gen-
eration.
Time quanta is defined as:
where Baud Rate is the binary value represented by
CNF1.BRP<5:0>
For some examples:
If FOSC = 16 MHz, BRP<5:0> = 00h, and Nominal Bit
Time = 8 TQ;
then TQ= 125 nsec and Nominal Bit Rate = 1 Mb/s
If FOSC = 20 MHz, BRP<5:0> = 01h, and Nominal Bit
Time = 8 TQ;
then TQ= 200 nsec and Nominal Bit Rate = 625 Kb/s
If FOSC = 25 MHz, BRP<5:0> = 3Fh, and Nominal Bit
Time = 25 TQ;
then TQ = 5.12 sec and Nominal Bit Rate = 7.8 Kb/s
The frequencies of the oscillators in the different nodes
must be coordinated in order to provide a system-wide
specified nominal bit time. This means that all oscilla-
tors must have a TOSC that is a integral divisor of TQ. It
should also be noted that although the number of TQ is
programmable from 4 to 25, the usable minimum is 6
TQ. Attempting to a bit time of less than 6 TQ in length
is not guaranteed to operate correctly
5.2
Synchronization Segment
This part of the bit time is used to synchronize the var-
ious CAN nodes on the bus. The edge of the input sig-
nal is expected to occur during the sync segment. The
duration is 1 TQ.
5.3
Propagation Segment
This part of the bit time is used to compensate for phys-
ical delay times within the network. These delay times
consist of the signal propagation time on the bus line
and the internal delay time of the nodes. The delay is
calculated as being the round trip time from transmitter
to receiver (twice the signal's propagation time on the
bus line), the input comparator delay, and the output
driver delay. The length of the Propagation Segment
can be programmed from 1 TQ to 8 TQ by setting the
PRSEG2:PRSEG0
bits
of
the
CNF2
register
The total delay is calculated from the following individ-
ual delays:
- 2 * physical bus end to end delay; TBUS
- 2 * input comparator delay; TCOMP (depends
on application circuit)
- 2 * output driver delay; TDRIVE (depends on
application circuit)
- 1 * input to output of CAN controller; TCAN
(maximum defined as 1 TQ + delay ns)
-TPROPOGATION = 2 * (TBUS + TCOMP +
TDRIVE) + TCAN
- Prop_Seg = TPROPOGATION / TQ
5.4
Phase Buffer Segments
The Phase Buffer Segments are used to optimally
locate the sampling point of the received bit within the
nominal bit time. The sampling point occurs between
phase segment 1 and phase segment 2. These seg-
ments can be lengthened or shortened by the resyn-
chronization process (see Section 5.7.2). Thus, the
variation of the values of the phase buffer segments
represent the DPLL functionality. The end of phase
segment 1 determines the sampling point within a bit
time. phase segment 1 is programmable from 1 TQ to 8
TQ in duration. Phase segment 2 provides delay before
the next transmitted data transition and is also pro-
grammable from 1 TQ to 8 TQ in duration (however due
to IPT requirements the actual minimum length of
phase segment 2 is 2 TQ - see Section 5.6 below), or it
may be defined to be equal to the greater of phase seg-
ment 1 or the Information Processing Time (IPT). (see
5.5
Sample Point
The Sample Point is the point of time at which the bus
level is read and value of the received bit is determined.
The Sampling point occurs at the end of phase seg-
ment 1. If the bit timing is slow and contains many TQ,
it is possible to specify multiple sampling of the bus line
at the sample point. The value of the received bit is
determined to be the value of the majority decision of
three values. The three samples are taken at the sam-
ple point, and twice before with a time of TQ/2 between
each sample.
5.6
Information Processing Time
The Information Processing Time (IPT) is the time seg-
ment, starting at the sample point, that is reserved for
calculation of the subsequent bit level. The CAN spec-
ification defines this time to be less than or equal to 2
TQ. The MCP2510 defines this time to be 2 TQ. Thus,
phase segment 2 must be at least 2 TQ long.
T
Q
2* Baud Rate + 1
()*T
OSC
=
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