TMC2072-MD SMSC, TMC2072-MD Datasheet - Page 50

• Manufacturer Part Number: TMC2072-MD
• Description: Network Controller & Processor ICs Peripheral Mode CircLink Cntlr
• Manufacturer: SMSC

Specifications of TMC2072-MD

• Product: Controller Area Network (CAN)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

2.11.3 Phase Error
Revision 0.1 (06-07-07)
NSTPRE[2:0]
000
001
010
011
100
101
110
111
Sending frequency and phase error in CM
The NST once set in the CS node will gradually drift out of synchronization as time progresses. This is
caused by differences between each XTAL. The less frequently the CM node sends packets, in other
words, the longer the sending interval is, the greater the phase deviates.
The NST resolution for a 16-MHz XTAL is 32 μs with the prescaler set to the intermediate (NSTPRE =
100). For the XTAL of precision 100 ppm, the phase error of maximum 200 μs per second occurs between
two nodes. The minimum period to cause the phase error of 32 μs (equals to a LSB of NST) is 0.16
(32/200) seconds. That is to say, if the CM node keeps sending packets every 160 ms or shorter, the
phase error of the CM and CS nodes can be kept within 32 μs. The following table shows the sending
intervals of the CM node that keeps the phase error within one LSB of NST:
The interval that the CM node can send packets within (TX Cycle of CM Node) is less than the time
required for all nodes to send full-size packets to the specific destination nodes at the same token rotation.
The time can be calculated with the following formula.
[ Calculation ]
( 352.5×br + 11×br×B ) × N
That is, if the rate is 2 Mbps under the 32 page, 32 byte mode, the CM node has the opportunity of sending
within 10.4 ms, which is calculated by (352.5 x 0.5 μs + 11 x 0.5 μs x 29B) x 31. That is frequent enough
against 160 ms in the above table on this page.
Communication speed (Data rate) and phase error
The time difference becomes longer as communication speed becomes slower. The reason for this is
because some data processing in CircLink such as a CRC check is dependent upon the data rate. The
relation between the transfer speed and time difference from CM to CS is listed as follows:
NST Resolution
128.0 (102.4) us =< 640 (512) ms
256.0 (204.8) us =< 1280 (1024) ms
16.0 (12.8) us =< 80 (64) ms
32.0 (25.6) us =< 160 (128) ms
64.0 (51.2) us =< 320 (256) ms
br: Bit cycle (br=400ns @2.5Mbps)
2.0 (1.6) us =< 10 (8) ms
4.0 (3.2) us =< 20 (16) ms
8.0 (6.4) us =< 40 (32) ms
16MHz(20MHz) XTAL
B: Number of Data Byte (Except header as SID, DID and C.P )
N: Node Number
TX Cycle of CM Node
DATASHEET
Page 50
NST Resolution
128.0 (102.4) us =< 640 (512) ms
16.0 (12.8) us =< 80 (64) ms
32.0 (25.6) us =< 160 (128) ms
64.0 (51.2) us =< 320 (256) ms
1.0 (0.8) us =< 5(4) ms
2.0 (1.6) us =< 10 (8) ms
4.0 (3.2) us =< 20 (16) ms
8.0 (6.4) us =< 40 (32) ms
32MHz(40MHz) XTAL
Peripheral Mode CircLink™ Controller
TX Cycle of CM Node
SMSC TMC2072
Datasheet