89s52 learning board (Difference between 74LS41 and 74HCT541

[sandeep_sggs]

89s52 learning board

Dear all,

m trying to build a 89s52 learning board. For programming the microcontroller m using the schematic attached. Instead of using 74HCT541, m using 74LS541.
M neither able to read the uc nor read the signature. Can anybody tell me what is the problem? M using a Xtal of 11.0592Mhz and two 33pf capacitors for clock generation.
Is it like 74LS541 creating the problem. What is the difference between 74LS541 and 74HCT541.

 

[Jack// ani]

89s52 programer problem????

Yea, true 74HCT541 is used to increase signal drive of parallel port.

I don't find any reason for it being called a complex circuitry. Because placing NOT 74HCXX glue logic instead of buffer is not going to reduce this complexity in any way.

Although there is no reason why you can not do it!

Hope this helps

 

[erio]

Re: 89s52 programer problem????

for separating printer port and uC circuitry.

 

[erio]

Re: 89s52 learning board

Hi! The main thing is switching voltage value. LS series are working like an ordinary TTL ("L" below 0.8, "H" from 2.4 up to VCC). HC series is working like CMOS ("L" below 0.8V, "H" - I am not quite sure - about 90% of VDD). The next is power consumption. But I think you can find details using f.e. Google web site.
Most NMOS accept TTL level on its inputs and can drive one TTL load on its outputs. Some CMOS accept TTL level, but some others not.
Also same devices from different manufacturers can have different input or output levels. Also different pins on a device can have different input or output levels. To drive HC from LS or NMOS you need pull up resistors.
I prefer HCTL but sometimes I have been using HC instead of HCT. Sometimes I have been using LS instead of HCT. But all depends on your application.

Sounds really confusing ?
Yes, no common rule exist !
So you must compare the data sheets of every device, which you want to use.