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From: conway@hplb29a.HPL.HP.COM (Daniel F. Conway)
Newsgroups: comp.sys.cbm
Subject: Re: C64 RS232 TTL Interface
Message-ID: <1740004@hplb29a.HPL.HP.COM>
Date: Wed, 7-Oct-87 15:02:44 EDT
Article-I.D.: hplb29a.1740004
Posted: Wed Oct  7 15:02:44 1987
Date-Received: Sun, 11-Oct-87 13:51:08 EDT
References: <4534@burdvax.PRC.Unisys.COM>
Organization: hplabs bld 29 Palo Alto
Lines: 20


  I need some clarification about the active levels on the user port
  of the C64 when used as a TTL-level RS232 port.


    I am trying to interface to
  an old Racal 212 modem which requires bipolar RS232 levels, and am trying to
  determine which signals need extra inverters (1488/1489 IC's both invert).

Rather than fool around trying to drive an RS232 device with TTL levels,
just get a good level converter that plugs into the C-64.  I use one from
Jameco, 1355 Shoreway Road, Belmont CA, (415) 592 8097; it works quite
well.  It is listed on page 46 of their 1988 catalog for $39.95.
The adapter  has switch-selectable polarities for the
modem control lines; using it with a good breakout box makes
interfacing rather easy (for RS-232, that is :-(  ).

Dan Conway
hplabs!conway
Palo Alto, California