COM20019 Datasheet, PDF(23/81 Page) SMSC Corporation – Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

COM20019 Datasheet, PDF (23/81 Pages) SMSC Corporation – Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM

◁

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

IMPEDANCE

ATTENUATION PER 1000 FT.

AT 5 MHz

5.5dB

7.0dB

5.5dB

150

7.0dB

100

17.9dB

105

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

is stored in the ROM and the instructions are

The COM20019 contains an internal fetched and then placed into the instruction

microsequencer which performs all of the control registers. One register holds the opcode, while

operations necessary to carry out the ARCNET the other holds the immediate data. Once the

protocol. It consists of a clock generator, a 544 x instruction is fetched, it is decoded by the internal

8 ROM, a program counter, two instruction instruction decoder, at which point the COM20019

registers, an instruction decoder, a no-op proceeds to execute the instruction. When a no-

generator, jump logic, and reconfiguration logic.

op instruction is encountered, the microsequencer

enters a timed loop and the program counter is

The COM20019 derives a 625 kHz and a 312.5 temporarily stopped until the loop is complete.

kHz clock from the output clock of the Clock When a jump instruction is encountered, the

Multiplier. These clocks provide the rate at which program counter is loaded with the jump address

the instructions are executed within the from the ROM. The COM20019 contains an

COM20019. The 625 kHz clock is the rate at internal reconfiguration timer which interrupts the

which the program counter operates, while the microsequencer if it has timed out. At this point

312.5 kHz clock is the rate at which the the program counter is cleared and the

instructions are executed. The microprogram MYRECON bit of the Diagnostic Status Register is

set.

DISCONTINUED DATASHEET

▷