Subject: Re: [TINI] LCD on TINI 10/20/50 board & related issues
Date: Wed, 02 Aug 2000 12:01:28 -0600
From: Bruce Boyes
To: tini@ibutton.com
At 12:33 8/2/2000 +0100, you wrote:
>Hi,
> I've just started playing with the Tini and the standard E10 Socket
>board. I was wondering if I can attach an LCD screen to this or whether I
>need the E50 board. If I can attach an LCD directly, does anyone have any
>pointers as to how this would be done? (I'm assuming it would be through the
>Parallel IO)
>
>Thanks very much for any help
>
>Barnaby Relph
Good question. I don't know how to attach an LCD to SocketPlus using
standard sockets or standoffs (yes - I have tried it), a standard 20x4 LCD
collides with other components on the board. A short cable seems a better
option, but:
The LCD interface is unbuffered - right on the high-speed data bus of TINI,
so you need to be careful. An e10 or e20 board doesn't have much else on it
so an LCD with a short cable (6" or less) should be OK. I haven't tried
this. I have tried plugging a 20x4 LCD right into an e50, with soldered
pins on the LCD (it sticks off e50 at a right angle). This is OK for
testing the LCD interface but not generally useful. The e50 has a lot of
other data bus loads on it and I would not recommend using a cable more
than an inch or three long to the LCD - adds too much capacitance and
inductance to the data bus with resulting signal degradation. e50 is
already close to the recommended load of the C390 controller. (Yes, I have
done analysis and testing to support this - as any system engineer
designing with TINI should - with any high speed controller you shouldn't
just start throwing loads at it without even adding them up, or considering
timing requirements).
and pleas to not flame me: I know that the issue of TINI bus
loading is a touchy subject and has not been officially documented by
Dallas. I'm trying to not make any wild or irresponsible claims here. I'm
trying to be careful what I say and can back up my statements with data.
Dallas should be the official source of information, and I am not speaking
on their behalf. We are designing with TINI so had to do our best to figure
these things out until such time as there are official TINI specifications.
We sell the e50 board and other sockets boards. Part of our support of
these products is trying to be honest with customers about what will and
won't work, to the best of our knowledge.
Maybe I should actually try this and post some scope photos and other results?
If you walk up to an LCD frame and touch it, you could crash the TINI with
an ESD surge to the data bus. I've done this on similar '8051 with LCD
systems', haven't tried to do it on TINI. On our commercial and custom
systems we make sure to ground the frame of the LCD well, and often cover
the display with a window or recess the metal bezel behind a frame so that
it can't be easily touched. Same thing applies to keypads.
In my opinion, for all these reasons, an LCD interface on TINI should be
buffered from the TINI signals.
We are putting our money where our mouth is - the SBX2 card
(http://www.systronix.com/expansion/sbx1.htm)
has a Xilinx CPLD which buffers all the signals, presenting only one CMOS
load to TINI. It also does the timing for the LCD, so that TINI can execute
a memory mapped write at full speed, and then goes on its way. The LCD
cycle timing is slower than a full speed TINI cycle, plus then the LCD
takes typically 20-40 usec to process a character, there's no need to make
TINI wait around for this. SBX2's CPLD deals with the LCD slowness (slow
relative to TINI and most high speed controllers). SBX2 is intended to work
with an LCD on at least a 12" ribbon cable.
One other note about LCDs - they are VERY high impedance devices. Also the
LCD assembly can be permanently damaged by washing, especially if any
minute amounts of contaminants are washed into the LCD module. Soldering to
the LCD should be done very carefully. We use special "no clean" flux
solder. I've seen poorly soldered and cleaned LCDs grow whiskery looking
structures around the connector pins after several months, and these have
enough conductivity to affect the operation. LCD data for 20x4 is online
at http://www.systronix.com/access/lcd.htm
Your mileage may vary, these are my opinions and may not be shared by others.
- Bruce
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Pretty nice socket boards & accessories for TINI Java
/\/\/\/ Systronix /\/\/\/
Complete Systems for Rapid Embedded Control Development
tel:801.534.1017 fax:-1019 http://www.systronix.com
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