Navigation bar
  Start Previous page
 129 of 156 
Next page End 124 125 126 127 128 129 130 131 132 133 134  

123
Appendix B - ZX-24 Series Hardware Reference
The heart of the ZX-24 is the Atmel AVR ATmega32 microcontroller while the ZX-24a is based on the
ATmega644 microcontroller.  The ZX-24p and ZX-24n devices are based on the ATmega644P
microcontroller.  In all cases, the microcontroller chip is accompanied by some support circuitry on a 24-
pin module that is simple to connect for operation.
The primary difference between the ZX-24 and the ZX-24a is the amount of RAM available for use by
your programs.  For the ZX-24 the User RAM comprises 1536 bytes (1.5K bytes) while it is 3.5K bytes for
the ZX-24a and ZX-24p.  The remainder of the microcontroller’s RAM is used by the ZX control program.
The ZX-24 also provides 992 bytes of internal EEPROM (electrically erasable programmable read-only
memory), referred to as Persistent Memory.  The ZX-24a and ZX-24p provide 2016 bytes of Persistent
Memory available to your program.  Data written to Persistent Memory is retained when the ZX is
powered down or reset.
The 24-pin ZX models provide additional Flash memory external to the microcontroller chip in which,
except for the ZX-24n, your program code is stored.  The ZX-24n has the external Flash memory but it is
not used because your program’s code is stored in internal Flash memory.  For all 24-pin ZX models, the
external Flash memory is 32K bytes in size.
The ZX-24 and ZX-24a have 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 the resources may be accessed directly using built-in
registers.  See Section 3.8.1 for more information on this topic.
B.1 External Connections
The ZX-24 series devices can be hooked up in several different ways depending on your requirements. 
The simplest method is depicted below.  The connector on the left is the serial connection to your PC for
downloading code and transmitting/receiving data on serial channel 1.  The connection to pin 3 of the ZX-
24 series is only needed for downloading.  You may wish to add a jumper in that line so that it may be
disconnected for “normal” operation.  Some operating systems, notably Windows XP, toggle the DTR line
(pin 4 of the DB-9) on the serial ports during boot up.  This will cause the ZX to reset on every positive-
going transition of the DTR line.
Simple ZX-24 Series Interconnection
Previous page Top Next page