COM20020D Datasheet, PDF(22/72 Page) SMSC Corporation – ULANC Revision D Universal Local Area Network Controller with 2K x 8 On-Board RAM

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COM20020D Datasheet, PDF (22/72 Pages) SMSC Corporation – ULANC Revision D Universal Local Area Network Controller with 2K x 8 On-Board RAM

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CABLE TYPE

RG-62 Belden #86262

RG-59/U Belden #89108

RG-11/U Belden #89108

IBM Type 1* Belden #89688

IBM Type 3* Telephone Twisted

Pair Belden #1155A

COMCODE 26 AWG Twisted

Pair Part #105-064-703

Table 1 - Typical Media

NOMINAL

ATTENUATION PER 1000 FT.

IMPEDANCE

AT 5 MHz

93â¦

5.5dB

75â¦

7.0dB

75â¦

5.5dB

150â¦

7.0dB

100â¦

17.9dB

105â¦

16.0dB

*Non-plenum-rated cables of this type are also available.

Note: For more detailed information on Cabling options including RS-485, transformer-coupled RS-485

and Fiber Optic interfaces, please refer to TN7-5 â Cabling Guidelines for the COM20020 ULANC,

available from Standard Microsystems Corporation.

FUNCTIONAL DESCRIPTION

MICROSEQUENCER

instructions are fetched and then placed into the

The COM20020D contains an internal instruction registers. One register holds the

microsequencer which performs all of the control opcode, while the other holds the immediate data.

operations necessary to carry out the ARCNET Once the instruction is fetched, it is decoded by

protocol. It consists of a clock generator, a 544 x the internal instruction decoder, at which point the

8 ROM, a program counter, two instruction COM20020D proceeds to execute the instruction.

registers, an instruction decoder, a no-op When a no-op instruction is encountered, the

generator, jump logic, and reconfiguration logic.

microsequencer enters a timed loop and the

program counter is temporarily stopped until the

The COM20020D derives a 10 MHz and a 5 MHz loop is complete. When a jump instruction is

clock from the output clock of the Clock Multiplier. encountered, the program counter is loaded with

These clocks provide the rate at which the the jump address from the ROM. The

instructions are executed within the COM20020D. COM20020D contains an internal reconfiguration

The 10 MHz clock is the rate at which the program timer which interrupts the microsequencer if it has

counter operates, while the 5 MHz clock is the rate timed out. At this point the program counter is

at which the instructions are executed. The cleared and the MYRECON bit of the Diagnostic

microprogram is stored in the ROM and the Status Register is set.

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