20X2 5v at 3v3?

M

MartinM57

Moderator
Just checking...for the first time ever, I'm going to run a 3v3 (throughout) system.

1. According to http://www.picaxeforum.co.uk/showthread.php?t=8609, I can run a 5v 20X2 at 3v3?

2. I can use an AXE027 and the normal download circuit to program?

3. Sertxd commands will result in successful comms back to the PC via the AXE027?

4. If I need a MAX232-alike inversion between 20X2 and PC, I can't use a MAX232 as they are for +5V supplies. So what do I use?

Any other gotcha's?

Ta, Martin
 
E

eclectic

Moderator
20X2 / 2 Alkaline (~3.05v) / AXE091 / AXE027

Code: 
main:
for b0 = 0 to 255
sertxd (#b0," ")
pause 40
next
goto main
Downloaded and ran fine.

3/4

Max232? Pass.

e
 
hippy

hippy

Ex-Staff (retired)
I tend to always run my AXE090 development board and all PICAXE's on 3V3 just to save any embarassing accidents should I plug a 28X2-3V or 40X2-3V in and forget to change the PSU voltage ... absolutely no problems whatsoever.

Apart from the TOPS18 IR Reciever chip which needs 5V.

The standard download interface ( 10K, 22K ) is okay for AXE027 and for direct serial port connection. SERTXD works okay for both.

The AXE090 uses a MAX202CPE ( two-zero-two ) and that seems to work when using 3V3 or 5V. I've never measured the serial line voltages though.
 
A

Andrew Cowan

Senior Member
The hot air station is working wonderfully - I've had sucess soldering PLCC LEDs, SOICs, QFPs, SOT-23s, TSSOPs, QFNs - even a few leadless devices. The station is still working flawlessly - I'd highly recommend one.

A
 
W

westaust55

Moderator
@MartinM57,

the PIC 18F14K22 datasheet (still advance info status) states:

Absolute values as:
Voltage on VDD with respect to VSS, PIC18F1XK22 ..... -0.3V to +6.0V

and further on under operating conditions:
PIC18F1XK22 Supply Voltage
1.8 - 5.5 Vdc and FOSC < = 20 MHz
2.7 - 5.5 Vdc and FOSC < = 64 MHz &#8804; 85°C
2.7 - 5.5 Vdc and FOSC < = 48 MHz &#8804; 125°C
 
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