ZBasic and ZX microcontrollers.
Powerful microcontrollers for engineers, scientists, experimenters and hobbyists.

ZX-24a Microcontroller


ZX-24a Microcontroller
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Note: the ZX-24a is out of stock and has been discontinued. We recommend the ZX-24r as a replacement. If you have a specific need for the ZX-24a, please contact us for further information.

The ZX-24a is a powerful microcontroller for your home automation, industrial control, robotics or other embedded systems application. It is an expanded-capacity version of the popular ZX-24 microcontroller, the primary difference being an additional 2K of User RAM. The ZX-24a also supports pin-change interrupts on all of the I/O lines.

The heart of the ZX-24a is the Atmel AVR ATmega644 microcontroller running at 14.7MHz. It is accompanied by some support circuitry on a 24-pin DIP module that is pin-compatible with the Parallax Basic Stamp and NetMedia BX-24 microcontrollers. However, many advances have been made with respect to those pioneering products in order to provide a more powerful and flexible programming platform.

The ATmega644 microcontroller internally has 4096 bytes of RAM of which 3584 bytes (3.5K) are reserved for direct use by your programs (including dynamically allocated string data). The remaining 512 bytes are used by the ZX-24a's control program. The mega644 also has 2048 bytes of internal EEPROM of which 2016 bytes are usable by your program for non-volatile storage. The 64K byte internal Flash memory of the Mega644 is used solely by the control program of the ZX-24a, also known as the Virtual Machine (VM). User programs are stored in a 32K byte EEPROM on the ZX-24a. This memory can also be used for storing data (both read-only and read/write) in addition to your program's code.

The Mega644 has other resources available to your program including a high-speed serial port, analog-to-digital converters, timers and other sub-systems that may be accessed using routines in the ZBasic System Library. Alternately, some of these resources may be accessed directly using built-in registers.

You may download a schematic of the ZX-24a (identical to that of the ZX-24) as a PDF or as an ExpressPCB .sch file. To view the latter, you'll have to download free software from ExpressPCB.

Technical Features
  ZX-24a BX-24P BS-2IC
Manufacturer Elba Corp. Netmedia, Inc. Parallax, Inc.
Package 24-pin DIP 24-pin DIP 24-pin DIP
Operating Temperature -40 to +85C -40 to +85C 0 to +70C (industrial version available)
Processor Atmel AVR ATmega644 Atmel AVR ATmega8535 Microchip PIC 16C57C
Power Requirements 4.5-5.5VDC regulated or 7-20VDC 3-5.5VDC regulated or 5-24VDC 5VDC regulated or 5-15VDC
Processor Speed Up to 14.7MIPS (14.7MHz) Up to 7.35 MIPS (7.35MHz ) Up to 5MIPS (20MHz)
Program Execution Speed Up to 175,000 instructions/sec Up to 83,000 instructions/sec ~4,000 instructions/sec
User RAM 3584 bytes 401 bytes 32 bytes
Non-volatile Data Memory 2016 bytes 480 bytes None
Program Memory 32K bytes (8000+ instructions) 32K bytes (8000+ instructions) 2K bytes (~500 instructions)
Digital I/O pins 16+3 (note 4) 16+3 (note 4) 16
Analog-to-Digital Channels Up to 8 channels, 10-bit Up to 8 channels, 10-bit None
PWM Channels Two 16 bit Requires application code One 8-bit pseudo-PWM
I2C Support 1 HW channel, 4 SW channels Requires application code 2 SW channels
1-Wire Support Bit and byte level Bit level only Bit and byte level
SPI Support 4 HW channels 4 HW channels No
Synchronous Serial I/O Support 1-16 bits, MSB or LSB first 1-8 bits, MSB first only 1-16 bits, MSB or LSB first
Asynchronous Serial I/O Ports 1-HW, up to 4 SW full duplex 1-HW, 1 SW full duplex 1-HW, half duplex SW on any I/O pin
X-10 Command Support Yes Yes Yes
Multi-tasking Support Yes Yes No
External Interrupts 3 1 None
Pin Change Interrupts All I/O lines No No
Analog Comparator Interrupt Yes No No
Interval Timer Yes No No
Exception Handling Support Yes No No
On-board LEDs Red, Green Red, Green None
Floating Point Math Yes - IEEE 32-bit Yes - IEEE 32-bit No
Advanced Floating Point Functions (sin, cos, log, etc.) System Level User Level No
Programming Interface Serial - 115.2K baud Serial - 115.2K baud Serial - 9600 baud
Field Upgradeable System Software Yes No No
  1) Items in boldface indicate differences from the ZX-24.
  2) Information from manufacturer's documentation and website.
  3) Maximum speed based on the instruction b = b + 1 with stack checking disabled.
  4) The additional 3 I/O lines are outside of the standard 24-pin DIP format.
  5) SW means implemented in system software, HW means hardware implementation.
  6) 'User Level' implementation adds code to the compiled program and is slower than 'System Level' implementation.
  Specifications subject to correction and change without notice.

A standard serial port is required to download code to the ZX-24a. If your computer does not have a standard 9-pin serial port but does have a USB port, you may use a USB to serial adapter. Note, however, that some USB to serial adapters are too slow to be useful with the ZX microcontrollers. We have found that adapters based on the second generation FTDI chips seem to work well.

The ZBasic IDE, compiler and documentation may be obtained free of charge via the Download page. See the menu at the left.

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