[TI-H] Re: PIXpander

To: ti-hardware@lists.ticalc.org
Subject: [TI-H] Re: PIXpander
From: Adam Thayer <krevinek@matrix-z.net>
Date: Fri, 4 May 2001 20:29:12 -0700 (PDT)
Reply-To: ti-hardware@lists.ticalc.org

--- Stephan Effelsberg <b012414@dvz.fh-koeln.de>
> wrote:
>Hello folks,
>did anybody try to get Sami's PIXpander working (sami.ticalc.org)?
>If there are some of you who also tried it and didn't get it working
>here are some hints:
>1. There's a bug in Sami's schematic. The positions of the button and
>the corresponding resistor must be exchanged. The program expects a high
>signal when the button is pressed, but in the schematic it works the
>other way round.

Okay, seems reasonable... one of the reasons why we should all bread-board our projects first. I have been working on this project, minus a programmed PIC (I had problems hacking my COM84 Programmer together, to find out there was *NO* problem) and a 4Mhz Crystal, so I don't know if this is correct or not. Sami MAY actually expect the high signal for a 'wait' loop signal, hmm.....

>3. Non-Sony memory cards may require the 7.5V power supply. My card
>(which is in fact an imitation) didn't work without.

I realize that too, and don't personally have the problem, BUT there is a work-around...
Hook up a 7.5V or a 7.2V or whatever you can grab and hook it up so that VIN (the 7.x V part) is on the +7V pin on your connector, VOUT is to your positive battery, and GND is hooked to the other end of the battery (Seperate from the project's GND).  If you don't need this workaround, don't, since you are WASTING electricity doing so to power the regulator. 

>What works for me, and what doesn't?
>1. If I try to send data from the calc to the PIXpander, the LED starts
>blinking. This means that the header has been sent properly. However, if
>I push the button the PIXpander only makes a few number of actions and
>returns to the main loop, the calc responds with a transmission error.

Hmm... I will have to check into this one, but that is kinda odd. One person did e-mail onto TI-H or the IRLink list saying that they DID get one of these suckers working... it sent perfectly, but recieving back from the card was somewhat muggy. That said, I will endeavour to get this baby working myself this weekend once I get my final part (the 4Mhz crystal) and test it with a RadioShack Sony-Compliant 1M card and a 24 Page card that only uses the 3.3-3.5V signal.

However, I do have one burning question about the schematic. Why are all the signals to the card (CLK, ACK, SEL, CMD, DAT) based on 5V? Also, why isn't SEL just hooked to ground? SEL being low tells the card that it is selected for communication. Why would it not?


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