ZBasic Language Reference
216
ZBasic Microcontrollers
Clock Source
The ZX-128a1n device requires 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 91 and 92 along with the necessary
capacitors. Some recommended crystals are shown in the table below.
Recommended Crystals
Package
Crystal
HC-49/US
ECS-147.4-20-4X (Digi-Key #X1102-ND)
HC-49/U
ECS-147.4-20-1X (Digi-Key #X1032-ND)
Cylinder
ECS-147.4-18-9X (Digi-Key #XC-1382-ND)
ZX-128a1 Clock Source
If you already have a clock source at the required frequency you can feed that signal directly to pin 92. In
this case there would be no connection to pin 91.
Serial Interface
The ZX-128a1 device requires a serial interface for downloading code into Program Memory and for your
program’s use via Com1. The recommended serial interface circuitry is shown below. This circuit has
two sub components. The MAX3232E chip functions as an RS-232 level converter that translates the 0-
3.3 volt signals of the ZX-128a1 to the standard RS-232 voltage levels.
The second component is the ATN circuitry that is used to signal the ZX-128a1 to go into download
mode. The latter circuitry is that portion connected between pin 4 of the DB-9 serial connector and pin 90
of the ZX-128a1. 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-128a1 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-128a1 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 MAX3232E chip includes a DC-DC
converter that produces nominally +/- 10V from a 3.3 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
MAX3232E while the negative voltage is available on pin 6. Consult the datasheet for the MAX3232E
device for information on the current capacity of these supplies.
The PDI_DATA pin of the ZX-128a1 (pin 89) is used for factory programming and should be left
unconnected.
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