COM20020I-DZD-TR Standard Microsystems (SMSC), COM20020I-DZD-TR Datasheet - Page 21

• Manufacturer Part Number: COM20020I-DZD-TR
• Manufacturer: Standard Microsystems (SMSC)

Specifications of COM20020I-DZD-TR

• Number Of Transceivers: 1
• Operating Supply Voltage (max): 5.5V
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (min): 4.5V
• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 28
• Lead Free Status / RoHS Status: Compliant

5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM
Datasheet
5.2
5.2.1
Note:
5.2.2
SMSC COM20020I Rev D
In the MOTOROLA CPU mode (DIR, nDS mode), the same modifications apply.
Transmission Media Interface
The bottom halves of Figure 5.1 and Figure 5.2 illustrate the COM20020ID interface to the transmission
media used to connect the node to the network. Table 5.1 - Typical Media on page 24 lists different types
of cable which are suitable for ARCNET applications.
of three ways:
Traditional Hybrid Interface
The Traditional Hybrid Interface is that which is used with previous ARCNET devices.
Interface is recommended if the node is to be placed in a network with other Hybrid-Interfaced nodes. The
Traditional Hybrid Interface is for use with nodes operating at 2.5 Mbps only. The transformer coupling of
the Hybrid offers isolation for the safety of the system and offers high Common Mode Rejection. The
Traditional Hybrid Interface uses circuits like SMSC's HYC9068 or HYC9088 to transfer the pulse-encoded
data between the cable and the COM20020ID. The COM20020ID transmits a logic "1" by generating two
100nSnon-overlapping negative pulses, nPULSE1 and nPULSE2. Lack of pulses indicates a logic "0".
The nPULSE1 and nPULSE2 signals are sent to the Hybrid, which creates a 200nS dipulse signal on the
media. A logic "0" is transmitted by the absence of the dipulse. During reception, the 200nS dipulse
appearing on the media is coupled through the RF transformer of the LAN Driver, which produces a
positive pulse at the RXIN pin of the COM20020ID. The pulse on the RXIN pin represents a logic "1".
Lack of pulse represents a logic "0".
COM20020ID can tolerate distortion of plus or minus 100nS and still correctly capture and convert the
RXIN pulses to NRZ format. Figure 5.4 illustrates the events which occur in transmission or reception of
data consisting of 1, 1, 0.
Please refer to TN7-5 – Cabling Guidelines for the COM20020 ULANC, available from SMSC, for
recommended cabling distance, termination, and node count for ARCNET nodes.
Backplane Configuration
The Backplane Open Drain Configuration is recommended for cost-sensitive, short-distance applications
like backplanes and instrumentation. This mode is advantageous because it saves components, cost, and
power.
Since the Backplane Configuration encodes data differently than the traditional Hybrid Configuration,
nodes utilizing the Backplane Configuration cannot communicate directly with nodes utilizing the
Traditional Hybrid Configuration. The Backplane Configuration does not isolate the node from the media
nor protects it from Common Mode noise, but Common Mode Noise is less of a problem in short
distances.
The COM20020ID supplies a programmable output driver for Backplane Mode operation. A push/pull or
open drain driver can be selected by programming the P1MODE bit of the Setup 1 Register (see register
descriptions for details). The COM20020ID defaults to an open drain output.
The Backplane Configuration provides for direct connection between the COM20020ID and the media.
Only one pull-up resistor (in open drain configuration of the output driver) is required somewhere on the
RBUSTMG BIT
0
1
Normal Speed CPU Read and Write
High Speed CPU Read and Normal Speed CPU Write
DATASHEET
Typically, RXIN pulses occur at multiples of 400nS.
Page 21
BUS TIMING MODE
1
The user may interface to the cable of choice in one
Revision 12-05-06
The Hybrid
The