gnupic: DIY USB programmer ?
Subject:
Re: DIY USB programmer ?
From:
Byron A Jeff ####@####.####
Date:
5 Jan 2005 16:36:38 +0000
Message-Id: <20050105163634.GA9424@cleon.cc.gatech.edu>
On Wed, Jan 05, 2005 at 09:19:15AM -0500, Byron A Jeff wrote:
A bit of snippage...
> 3. Now you tune the 555 delay to about 1/2 a character transmit time. This
> should be doable without any fancy equipment if you test with flip flop
> like the 74HCT74. Simply tie the transistor base to the D input of the FF
> and tie the output of the 555 to the clock (you may need to invert
> the signal). Then tune the delay resistor until when you send a 0x00 down
> the serial port you get one bit and when you send 0xff down the port you
> get the other bit.
You may not even need to do that. Consider if you tie the output of the
555 back to the RX for the serial port, with no inversion. If the USB cable
responds to a typical 0V-5V signal like ordinary PC serial ports, then you
can transmit back the 555 timing back through the serial port. The low output
is the standard idle state for the serial port, so when the 555 is triggered
it'll send a start bit and some number of zeros before returning to the idle
state. So testing should be as simple as sending 0xff to the serial port and
then reading back the result. When the result gets to somewhere between 0xe0
and 0xf8 then you know that the trigger is centered in the character cell.
So it should just take a small piece of test software to get things going.
I figure it can be a debug/setup feature of the actual programming software.
BAJ
