Couple questions

[jledger]

I'm in need to create an 8x8 keyboard matrix.
I figure the 28x will just handle the job.

I'm also curious if the serial out is TTL safe to tie to other chips, or if I should shove a MAX232 into the mix on receiving end?

 

[moxhamj]

There are all sorts of cunning matrix circuits - maybe have a search of the forum as a start but I'm sure others will contribute ideas.

Re the serial out - this is simply 0V/5V and will interface directly to any TTL/HC/CMOS etc chip with no need for a MaxS232. In fact, you don't even need any interface to a PC - the serial out can go straight into the RS232 input as the PC interprets 0V as 0 and anything more than 3V as a 1.

Edited by - Dr_Acula on 02/04/2007 05:52:31

 

[jledger]

I'm interfacing to another micrcontroller which is designed for 3v inputs. If I use a 10k resistor between the serial output and the input of the other chip I suspect it will do the job without harming the chip?

 

[hippy]

Probably, but you'd have to check the datasheet to determine what current flow it could handle.

Alternatively, use a resistive voltage divider, transistor ( or open-collector logic gate ), with pull-up and you can put a 3V zener across the input.

You won't need a MAX232 as an input buffer to the receiving micro, but you can add an extra level of protection by dropping the incoming 5V signal using one of the methods suggested and buffering it through a logic gate ( 3V supply ) into the receiving micro.

Edited by - hippy on 02/04/2007 15:06:15

 

[Dippy]

From PICAXE 5V O/P to a.n.other 3V device I/P a simple pot/div level shifter is the usual method.
I'll leave you to do the calcs.