quick question 40x2 wiring

[SeanHowson]

Hiya
Just a quick question I can't seem to fathem, I'm using a picaxe 40x2 with a 6v power supply, there seems to be two power terminals and grounding terminals, which two should I use? Which side of the chip should I use? (there is a +V and a 0V terminal on each side of the chip)

 

[srnet]

Use both sets of power pins.

Dont run the 40X2 at 6V, its intended to be used on 5.5V max.

 

[westaust55]

Don't forget to add a 100 nF ceramic capacitor across the power supply close to the PICAXE supply pins for decoupling (against electrical "noise" generated by transistors switching within the chip).

 

[Bill.b]

If you need to run the 40x2 from a 6v supply, include a diode (IN4001) in series with the supply.
This will reduce the voltage to the 40x2 to about 5.4volts.
Also this will protect the 40x2 from reverse voltage.
as westaust55 recommended, include a 100nf across the power terminal as well as a
lager electrolytic capacitor across the supply, a 100uf would be OK.

Bill

 

[westaust55]

There does not appear to be anything in PICAXE Manual 1 on the topic however, from the Microchip website:

Many PICmicro MCUs have more than one VSS or VDD pin. This is common on
devices with higher pin counts. These pins are generally connected internally but
through a finite impedance. To insure proper operation, all VSS and VDD pins need
to be properly connected externally.

And a few extracts on capacitors (from here):

2.2 Power Supply Pins
2.2.1 DECOUPLING CAPACITORS
The use of decoupling capacitors on every pair of
power supply pins, such as VDD, VSS, AVDD and
AVSS, is required.
Consider the following criteria when using decoupling
capacitors:
• Value and type of capacitor: A 0.1 uF (100 nF),
10-20V capacitor is recommended. The capacitor
should be a low-ESR device, with a resonance
frequency in the range of 200 MHz and higher.
Ceramic capacitors are recommended.
• Placement on the printed circuit board: The
decoupling capacitors should be placed as close
to the pins as possible. It is recommended to
place the capacitors on the same side of the
board as the device. If space is constricted, the
capacitor can be placed on another layer on the
PCB using a via; however, ensure that the trace
length from the pin to the capacitor is no greater
than 0.25 inch (6 mm).

2.2.2 TANK CAPACITORS
On boards with power traces running longer than
six inches in length, it is suggested to use a tank capacitor
for integrated circuits, including microcontrollers, to
supply a local power source. The value of the tank
capacitor should be determined based on the trace
resistance that connects the power supply source to
the device, and the maximum current drawn by the
device in the application. In other words, select the tank
capacitor so that it meets the acceptable voltage sag at
the device. Typical values range from 4.7 uF to 47 uF.