AN00012.TXT

Advanced Communication Board Developer's Toolkit 1995
    

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Subject: Maximum Data Rates for the ACB cards.

Maximum data rates on the ACB Family of cards are limited only by the
electrical interface, AT bus bandwidth, and the operating mode of the
SCC. The following is a listing of Maximum Data rates that are obtainable
on the SCC. Please refer to the notes at the end of this document for
more details.

				6MHz	8MHz	10MHz	16MHz	20MHz
Asynchronous Mode:
External Clock
    16X Mode (No BRG)		375K	500K	635K	1M	1.25M
BRG
    16X Mode (TX+0)		93.75K	125K	156.5K	250K	312.5K

Synchronous Mode:
External Clock (See Note 1)	1.5M	2M	2.5M	4M	5M
Using DPLL,FM encoding		375K	500K	625K	1M	1.25M
Using DPLL,NRZ/NRZI encoding	187.5K	250K


NOTE 1: Absolute Maximum data rates are obtained when using system DMA.
      Maximum DMA transfers are limited by the XT/AT bus bandwidth. Typically,
      the maximum data rates achievable on an AT style machine are between
      1.5 and 2M.

NOTE 2: The RS-232 specifies data rates of 20K at 50 feet. Although the
      maximum data rates obtainable with RS-232 are greater than 20K, if
      the line conditions are favorable, the limitations of the RS-232
      line drivers and receivers will be evident before the maximum data
      rate of the SCC is reached. To obtain SCC maximum data rates a
      combination of DMA and interrupts must be implemented. A differential
      interface, like RS-422 must be chosen before maximum data rates are
      achieved on the ACB Family of cards.