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From: bmiller@burdvax.UUCP
Newsgroups: comp.sys.cbm
Subject: C64 RS232 TTL Interface
Message-ID: <4534@burdvax.PRC.Unisys.COM>
Date: Fri, 2-Oct-87 16:12:32 EDT
Article-I.D.: burdvax.4534
Posted: Fri Oct  2 16:12:32 1987
Date-Received: Sat, 3-Oct-87 10:16:59 EDT
Sender: news@burdvax.PRC.Unisys.COM
Reply-To: bmiller@burdvax.UUCP (Bruce J. Miller)
Distribution: na
Organization: Unisys Corporation, Paoli Research Center; Paoli, PA
Lines: 21

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).
The C64 Programmers Manual shows which signal names are assigned to which pins
on the user port, but does not clearly indicate whether signals are active
TTL high or TTL low.  The signals of interest to me are:

From C64: TX DATA, RTS, DTR
To C64: RX DATA, CTS, CD (carrier detect), RI, DSR.

A clear description of which is the MARK state (for data) or ON state (for
control signals) would be very helpful. (Are you there, Fred Bowen?)

I am also curious as to whether most available terminal programs, including
Kermit, support a full handshaking interface, or contrarywise, what fraction
of a full interface is customarily supported.

Any and all help would be appreciated.

     Bruce (bmiller@burdvax.prc.unisys.com)