TMC2074-NE SMSC, TMC2074-NE Datasheet - Page 65

• Manufacturer Part Number: TMC2074-NE
• Description: Network Controller & Processor ICs Standalone Mode CircLink Cntlr
• Manufacturer: SMSC

Specifications of TMC2074-NE

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

Dual Mode CircLink™ Controller
Datasheet
2.14.2 Timer Expansion in Multi-stage Cascade Connection
NOTE:
SMSC TMC2074
Response Timer
An extra delay of 0.5 μs is added to the message when HUB is set to ON. A delay of 2.0 μs is also added
in the CMI coding/decoding processing when CMI is set to ON. When configuring a cascade connection
and setting both HUB and CMI to ON, a 2.5 μs (2.0 μs + 0.5 μs) delay is added to a message every time
the message passes a node.
This delay may make the response timer timeout in the CircLink, causing communication failure. The
response timer monitors responses from the nodes and is normally set to 74.6 μs. The one way
propagation delay time permitted for cable, HUB circuit, and CMI decoding/coding circuit is 31 μs, which is
calculated by (74.6 μs - 12.6 μs)/2; where 12.6 μs is the CircLink response time. This is equivalent to the
delay time of a 12-stage cascade connection HUB/CMI circuit.
(31μs / 2.5μs = 12.4 -> 12-stage)
If the sum of cable delay and HUB/CMI delay is over 31 μs, set ET1 to 0 to extend the response timeout
time to 298.4 μs, which is four times longer than the normal delay time. Taking this measures, the one way
propagation delay time is extended to (298.4 μs – 12.6 μs) /2 = 142.9 μs. (142.9μs / 2.5μs = 57.2 -> 57-
stage).
The timer can be set by the ET1 pin or internal register and has a structure of AND logic in the CircLink as
shown below.
Remarks:
The typical time delay added in ON state HUB is 0.5 μs. However, it is extended to 1.0 μs if the optical
mode is ON (nOPMD = L) and CMI is OFF (nCMIBYP = L).
Values in text and table are based on a 2.5 Mbps network speed. When CircLink operates at 1.25 Mbps,
the value should be doubled. When operating at 5 Mbps, the value should be half. To be precise, the
propagation delay time of the cable and the transceiver should also be added.
298.4uS
74.6uS
(default"1")
ET1 :Pin
ET1 :Register
DATASHEET
Idle Timer
328uS
82uS
Page 65
Configuration Timer
ET1
104mS
52mS
Revision 0.2 (10-23-08)