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000441_news@columbia.edu _Thu Mar 20 09:59:54 1997.msg
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From: Jeff_Wieland@ces.purdue.edu (Jeff Wieland)
Newsgroups: comp.protocols.kermit.misc,comp.os.cpm
Subject: Re: Back to Basics II (Blank screen in CP/M kermit)
Date: 20 Mar 1997 14:46:14 GMT
Organization: Purdue University Agricultural Computer Network
Lines: 51
Message-ID: <5grijm$erf@mozo.cc.purdue.edu>
References: <5gki33$8qi@sun.lclark.edu> <5gpk2t$e0p@mozo.cc.purdue.edu>
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In article <5gpk2t$e0p@mozo.cc.purdue.edu> Jeff_Wieland@ces.purdue.edu (Jeff Wieland) writes:
>In article <5gki33$8qi@sun.lclark.edu> miller@sun.lclark.edu (John Miller) writes:
>I'd be real suspicious that one or more of the line driver chips is
>blown. These chips convert between the TTL levels of the Z80 SIO and
>RS-232C levels. I blew one or two of them on my 2X once, and I got
>really weird results with a breakout box.
>
>Anyway, the '84 series Kaypros have 3 line drivers either two 1488's
>and one 1489, or two 1489's and one 1488. If you open up an '84 Kaypro,
>they are near the back of the motherboard by the serial ports (if your
>Kaypro has two serial ports, called serial data and serial printer, then
>its a '84 series). You could just replace them all, they're cheap.
To follow up my own post, there are in fact two 1489's (U3 and U5) and one
1488 (U4). U5 is used for RS-232 inputs by SIO-1, channel A, which is the
serial data port (J4 - SIO-2 channel A). This is probably the failed chip.
U4 (RS-232 output) is shared by both serial ports, and U3 is used only by
the serial printer port (J3). U4 MIGHT be the problem, and you might want
to replace it as well.
The lines used on J4 are:
1 tied to ground
2 TXD
3 RXD
4 RTS
5 CTS
6 pulled high through a 5.1K resistor
7 tied to ground
8 DCD
20 DTR
By the way, the serial printer port has ONLY the following connections:
2 RXD
3 TXD
20 CTS
SIO-1 channel B is connected to J2, the serial keyboard port, which has
the following connections:
1 +5 V
2 RXD
3 ground
4 TXD
SIO-2 channel B is used for the internal 300 bps modem that some '84
series Kaypro's have. Both of the B channels are fixed at 300 bps.
--
Jeff Wieland
Jeff_Wieland@ces.purdue.edu