TMC2072-MD SMSC, TMC2072-MD Datasheet - Page 93

• 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

Peripheral Mode CircLink™ Controller
Datasheet
Appendix A. CMI Modem
SMSC TMC2072
A-1 Outline
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 and CMI coding.
A-2 CMI Code
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
Figure 10 - CMI Coding State transition diagram
1
0
0
DATASHEET
1
Example:
1
Page 93
01
01
Data
0
0
CMI Code
Revision 0.1 (06-07-07)