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JTAG vs ISP/IAP

Started by zerealbigboss August 31, 2008
Can anyone tell me why I would use JTAG programming if I can do the
same, except debugging, with ISP/IAP? I wrote a very small
application (DOS/Windows98, Linux) for automated production
programming that works on 68HCs, PICs and the LPC2119 I am testing.

An Engineer's Guide to the LPC2100 Series

I think you already answered your own question with the "except debugging" ..

Other than that, your design may not have a need for bringing out an RS232 port (which requires a level shifter chip), so a JTAG
connector would be simpler.

(A programming cable that has a level shifter in it, like the RLC2 cables: http://www.piclist.com/techref/io/serial/RLC2.htm
wouldn't do since you would need RTS & DTR as well)

~ Paul Claessen

From: l... [mailto:l...] On Behalf Of zerealbigboss
Sent: Sunday, August 31, 2008 5:48 PM
To: l...
Subject: [lpc2000] JTAG vs ISP/IAP

Can anyone tell me why I would use JTAG programming if I can do the
same, except debugging, with ISP/IAP? I wrote a very small
application (DOS/Windows98, Linux) for automated production
programming that works on 68HCs, PICs and the LPC2119 I am testing.


Hello,

Am Montag, 1. September 2008 schrieb Paul Claessen:
> (A programming cable that has a level shifter in it, like the RLC2 cables:
> http://www.piclist.com/techref/io/serial/RLC2.htm wouldn't do since you
> would need RTS & DTR as well)
>

a nice and cheap option is to grab one of these cheap usb-cables for mobile
phones. They implement a serial port. While normally only RX/TX is put on the
cable to the phone, most of these adapters have RTS and DTR as well. Just
open the plug and put a "better" cable on, to carry the other signals.

That way i program my LPC2220 all the time, using RTS/DTR for reset and stuff.

> ~ Paul Claessen
>

Greetings,

Chris

On Sun, 31 Aug 2008 21:48:27 -0000, you wrote:

>Can anyone tell me why I would use JTAG programming if I can do the
>same, except debugging, with ISP/IAP? I wrote a very small
>application (DOS/Windows98, Linux) for automated production
>programming that works on 68HCs, PICs and the LPC2119 I am testing.

ISP is fairly slow due to a rather inefficient protocol and the baudrates supported.
IAP is significantly faster, but needs to have some software (e.g. bootloader) already in the chip
to do it.
JTAG has the advantage that you can use it to program a blank chip, however once you have your own
bootloader in the chip, you might be able to make it work faster then jtag with a suitably efficient
communications link and protocol. I don't know what the fundamental speed limits are for jtag, but
my guess is that the actual device programming time is going to be more of a limitation than the
comms speed, so any gains using an alternative protocol may not be worth the hassle.

>
>