TMC2074-NE SMSC, TMC2074-NE Datasheet - Page 104

• 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

Appendix A CMI Modem
A-1 Outline
A-2 CMI Code
Revision 0.2 (10-23-08)
Isolation by pulse transformers is widely used in this network. However, because in standard ARCNET
transmission the presence or absence of a pulse is indicated by 0 or 1, in data consisting of a sequence of
zeros such as 0x00 a prolonged succession of no pulses results in magnetic saturation of the transformer.
As a countermeasure, an external circuit on the standard ARCNET is designed to prevent magnetic
saturation (e.g. HYC4000). Because such an external component is not available in the CircLink external
circuit, where only a normal RS485 transceiver and pulse transformer are installed, a CMI modem circuit is
built in and converts the ARCNET into CMI coding.
In the CMI code the same value cannot continue for more than 2 bits.
The state it can take is decided, so it has a self-restoring function.
In CMI coding, input data is transitioned in 1-bit portions. Bits are indicated either as 11, 00, or 01. CMI
coding is carried out by making these into CMI coding symbols. At decoding, the process is the exact
opposite.
The CMI coding state transition diagram is shown below.
1
00
11
1
Figure 17 - CMI Coding State transition diagram
0
0
1
DATASHEET
Example:
1
01
01
Page 104
Data
0
0
CMI Code
Dual Mode CircLink™ Controller
SMSC TMC2074
Datasheet