Diacom plus on Pentium laptops

TBK terryk at foothill.net
Wed Jul 29 14:00:04 GMT 1998


Hi Ken,

I guess I wasn't clear on this. The parallel port, being bi-directional, is
a single connector that has enough I/O pins to allow all of the hardware
control to be handled in a simple manner. There is no "RS-232" per se from a
hardware standpoint. Well, old TTL RS-232 but that would be a mis-leading
statement.

The cable is just a few pull downs with the correct ALDL mode resistors and
some simple inverting buffers to get to the TTL levels of the parallel port.
The parallel port can source enough current to act as the supply voltage to
enable or disable each of the inverting input buffers. They can also talk
back out one of the inputs (bi-directional).

After going through it, it is pretty clever. There is nothing "new" in how
it is done, but Rinda did come up with a simple solution. Certainly you
could talk 8192 baud using the PC's serial port, but controlling the DIAG
line would require some other hardware.

I worked on talking 160 baud with the serial port and concluded the UART
can't be programmed to handle 9 bit data streams without overriding
everything.

I handled it by using a timer and interrupt to make a sampler. I would
sample the data stream at X2 the bit rate and then search for the 0->1
transitions, the 9-1's, the 9 data bits, drop the first bit, and stuff it in
a buffer. Repeat until the next 9-1's arrive.

Terry


-----Original Message-----
From: Ken Kelly <kenkelly at lucent.com>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>;
charset=iso-8859-1 at lucent.com <charset=iso-8859-1 at lucent.com>
Date: Wednesday, July 29, 1998 6:15 AM
Subject: Re: Diacom plus on Pentium laptops


>TBK,
>
>I believe you are correct on the 4 interfaces that Rinda is
>compatible with, but the Diacom cable would have to have a
>-10 to -12 volt supply to be able to create an RS-232
>signal. The Maxim chips now make that easy, but I don't
>think they were available when Rinda started the Diacom. Do
>you really think the Rinda cable attempts to actively shift
>levels? I thought the circuitry just shifted the pinouts
>around for the various standards.
> Ken
>
>TBK wrote:
>>
>> The C3 uses either the CE lamp (12V) or Serial 160 output 5V. P4 8192 is
5V.
>> The Diacom cable buffers the signal, so output voltage is not the reason
>> they use the parallel port. It is the best way to simulate a software
uart,
>> control the DIAG line modes and talk to three different hardware systems:
>>
>> C3 CE lamp
>> C3 Serial 160
>> P4 Serial 160
>> P4 8192
>>
>> Rinda crammed all of that into the circuit board in the cable.
>>
>> -----Original Message-----
>> From: Ken Kelly <kenkelly at lucent.com>
>> To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
>> Date: Tuesday, July 28, 1998 1:15 PM
>> Subject: Re: Diacom plus on Pentium laptops
>>
>> >The Diacom software runs on the Parallel port so it doesn't
>> >use a Uart. They use the Parallel port because the ALDL port
>> >does not have RS-232 voltages. You must use a level
>> >converter to convert the 0 to 5 volt signal to +/- 10 volts.
>> >Diacom uses the serial data link in the Parallel port
>> >because it has 0-5 volt levels. They do there own timing
>> >control.
>> >
>> > Ken
>> >
>




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