Lpc2000

Ed Schlunder wrote:

>I'm thinking of building the DIY wiggler so that I can program and
>debug some LPC2103 chips on the cheap.
>
>I see the wiggler.txt schematic in the files area. It is using a
>74AC244 chip to do voltage level conversion between the PC and the
>LPC21xx chip. It only seems to use 4 line drivers of the 74AC244 chip
>(half the chip is left unused). 
>
>Would there be any problem with using a 74VHC08 quad 2 input AND gate
>chip instead? I would just tie one side of each AND gate high so that
>it can be used as 4 line drivers. This chip is cheaper and smaller
>than the 74AC244.
>
>  
>
However, it may not have the same drive levels (output current).  The 
'244 series is a buffer / driver, typically producting 12ma sink and 4ma 
source.  The '08 is a logic device, not a driver,  you will probably 
only find that it can do +/- 4ma (if you are lucky).

Output impedance would dictate how quickly signals may be driven high / 
low on the JTAG interface.  Too high an impedance == lousy signal edges 
/ ring / overshoot.

TomW


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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