ZBasic Language Reference
200
ZBasic Microcontrollers
Clock Source
The ZX-1280 series devices require a clock source running at 14.7456MHz. The easiest way to provide
this clock source is to connect a crystal of that frequency to pins 33 and 34 along with the necessary
capacitors.
The recommended crystal to use is ECS-147.4-20-4 (Digi-Key #X175-ND). Alternate crystals are the
ECS-147.4-20-1 (Digi-Key #X142-ND) in a slightly larger package and the ECS-147.4-18-9 (Digi-Key
#XC-957ND) in a cylindrical package. The capacitor value to use depends somewhat on the layout (e.g.
stray capacitance). Values in the range of 22pF to 27pF have been used successfully in various
situations.
ZX-1280 Series Clock Source
If you already have a clock source at the required frequency you can feed that signal directly to pin 34. In
this case there would be no connection to pin 33.
Serial Interface
The ZX-1280 series devices require a serial interface for downloading code into Program Memory,
performing field updates of the control program, and for your programs use via Com1. The
recommended serial interface circuitry is shown below. This circuit has two sub components. The
MAX232 chip functions as an RS-232 level converter that translates the 0-5 volt signals of the ZX to the
standard RS-232 voltage levels.
The second component is the ATN circuitry that is used to signal the ZX to go into download mode. The
latter circuitry is that portion connected between pin 4 of the DB-9 serial connector and pin 30 of the ZX-
1280. You may want to include a jumper in the ATN circuitry so that it can be disconnected when
downloads are not required. With the ATN circuitry connected, the ZX will receive a reset pulse on every
positive transition of pin 4 (DTR) of the serial connector. If alternate component values are chosen you
must ensure that the ZX receives a reset pulse of at least 2uS on every positive transition of the DTR
signal on pin 4 of the serial connector.
One advantage to using this recommended circuit is that the MAX232 chip includes a DC-DC converter
that produces nominally +/- 12V from the 5 volt source. This is particularly useful if your application
requires one or more of these voltages. For example, some LCD devices require a low-current negative
supply for their backlight circuitry. The positive voltage is available on pin 2 of the MAX232 while the
negative voltage is available on pin 6. Consult the datasheet for the MAX232 device for information on
the current capacity of these supplies.
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