Serial I/O specifications

[Fred Cady]

There were some questions about serial I/O maximum cable runs.  Here's the
poop from the specs for RS232, RS422, RS423, and RS485.  A good source
of single powersupply conversion chips is Maxim.

We sure need somebody to come up with a TSR that will interface
CT with an ethernet.


Summary of RS-232C, RS-423, RS-422 and RS-485 Standards

Specification  RS-232-C     RS-423        RS-422         RS-485
------------------------------------------------------------------------
Receiver input +-3 to       +-200mV to     +-200mV to    +_200Mv to
voltage        +-15V        +-12V          +-7V          +-7V to +-12V
------------------------------------------------------------------------
Driver output  +-5 to       +-3.6V to      +-2V to       +-1.5V to
signal         +-15V        +-6V           +-5V          +-5 V
------------------------------------------------------------------------
Maximum data 
rate           20 Kb/s      100 Kb/s      10 Mb/s        10 Mb/s
------------------------------------------------------------------------
Maximum cable 
length         50 feet      4000 feet     4000 feet      4000 feet
------------------------------------------------------------------------
Driver source 
impedance      3 K to 7 K   450 min       100            54 
------------------------------------------------------------------------
Receiver input 
resistance     3 K          4 K  minimum  4 K  minimum   12 K minimum
------------------------------------------------------------------------
Mode           Single-ended Single-ended  Differential   Differential
------------------------------------------------------------------------
Number of 
drivers and 
receivers 
allowed on one 
line           1Dr/1Rx      1Dr/10Rx      1 Dr/10Rx      32Dr/32Rx
------------------------------------------------------------------------



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