Guide to PICAXE Selection


The chart below provides a convenient at-a-glance view to compare and contrast PICAXE microcontrollers based on some of the most significant considerations in chip selection. See the notes which follow for important information to help you understand the chart and choose the most appropriate PICAXE for your project.

Chip
Size/Type
Program
Memory
Data
Memory
Scratchpad
Memory
Max.
Clock
Speed
InputsOutputsADCTouch
Sensor
Ready
0840-110128-prog04 MHz1-41-41 lowNo
08M80-220256-prog08 MHz1-41-43No
14M80-220256-prog08 MHz652No
18M2600-1800256032 MHz1-131-1313Yes
20M80-220256-prog08 MHz884No
20X21000-320025612864 MHz1-161-159No
28X11000-320012812820 MHz1-129-174No
28X21000-3200 256102464 MHz1-201-2019Yes
40X11000-320012812820 MHz8-209-177No
40X21000-3200 256102464 MHz1-271-2627Yes


Notes and Additional Considerations

The first number in the chip type designation indicates the number of pins - a PICAXE 08M has 8 pins and a 28X2 has 28 pins.

PICAXE types 18, 18A, 18M, 18X, 28A, 28X and 40X are obsolete. Those chips are not recommended for new designs and are therefore not listed here. Additionally, Revolution Education has released upgraded 28X2 and 40X2 devices. Although the PICAXE part number remains the same, these chips are based on newer Microchip Technology processors and can be distinguished from the older chips by the labels: the new 28X2 is labeled 18F25K22 and the new 40X2 is labeled 18F45K22. The new chips represent a significant upgrade with faster clock speeds, more ADC channels, support for touch technology, and enhancements to the PWM features. The new chips also operate across a wider voltage range and therefore there are no longer low and high voltage variants.

Program memory is expressed in lines of code. Program memory must be stated as a range because some commands use more memory than others. X2 chips support multiple program slots in which program memory can be allocated across multiple programs. The 28X2 and 40X2 can support up to four different programs using onboard program memory. All of the X2s can support as many as 32 program slots using external EEPROM. The new M2 series features a multitasking capability in which up to four separate programming tasks can be executed in parallel.

Data and scratchpad memory is expressed in bytes. On M series chips data memory is shared with program memory. On the chart you will therefore see data memory expressed as a number of bytes minus whatever has been consumed by the program. On 18M2 the upper 256 bytes are shared between program and data (2048 in total). For programs that are less than 1792 bytes long all 256 bytes of data memory are available - programs longer than 1792 will begin to consume data memory. In X series chips the data memory is distinct and therefore the entire amount listed is available.

i2c enabled chips are able to interface with a number of i2c compliant devices including EEPROM memory which provides access to large amounts of data storage.

On some chips certain pins can be configured as either input or output. On these chips the number of inputs or outputs is expressed as a range.



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