On Fri, 01 Aug 2008 11:29:26 -0400, legg wrote:

On Thu, 31 Jul 2008 15:02:57 +0930, "mark krawczuk"
wrote:

hi, i`m trying to build a bdm32 interface to program my saab trionic ecu ,
put the parts list is for hc ttl ic`s , i have ls ttl ic`s , are these
interchangable ?
thanks,

I believe AC and AHC were developed to be more TTL compatible. The
problem is input logic level recognition.

---
That's true on the CMOS side, but I think AC and AHC were developed
for higher speeds than available in HC and HCT, HCT and ACT being
developed to allow compatibility with bipolar TTL outputs.

TI recommends a pullup to Vcc on the TTL part to remove the
incompatibility, with a value of:


Vcc - TTL Vol(max)
R = ---------------------
TTL Iol + n CMOS Il


JF