ZBasic Language Reference
180
ZBasic Microcontrollers
Pin 22, Reset
You may apply an active low signal to this pin to reset the processor. Note, however, that the on-board
reset circuitry will also pull this line low via an open collector output each time the ATN input makes a
positive transition (notably during downloading). If you don’t want your external circuitry to receive this
reset signal, you must isolate the on-board reset from external devices using a diode, a transistor or an
open collector gate. An example circuit is shown in Section D.1.
Pin 23, Ground
This pin, common with pin 4, serves as the reference for the power supply and all I/O pins.
Pin 24, Unregulated Voltage In
To use the on-board regulator, you may supply an unregulated (but filtered) voltage source from 7 to 20
volts DC to this pin. The power supply must be capable of supplying at least 150mA. See the description
of pin 21 for more information about the on-board regulator and the limitations of using it. It is important
to note that the maximum input voltage must be derated above an ambient temperature of 45°C
according to the formula V
in
<= 5 + (125 – T
amb
) / 5.2. For example, with an ambient temperature of 75°C
the input voltage must be kept below 14.6V. For operating in high ambient temperatures it is
recommended to use an external regulator with an appropriate heatsink.
Additional Notes:
Each of the I/O pins (5-20, 25-27) can source 20mA or sink 40mA (at Vcc=5V). However, the total source
current and the total sink current for all pins may not exceed 200mA. This is further limited by the
capacity of the on-board regulator if it is being used. At Vcc=3V, the maximum source and sink currents
are one-half of the 5V rating.
All of the I/O pins (5-20, 25-27) have protection diodes built in. If the signals that you connect to these
pins go above V+ or below ground, you must include a current limiting resistor to keep the pin current
below 20mA.
D.2.2 Expansion Pins
The table below summarizes the functions of the ZX-24 series expansion pins. These “pins” are actually
holes on the circuit board that require a soldered or mechanical clip connection to use. A detailed
description of each pin is given following the table.
Expansion Pins
Pin
ATmega
ATxmega
25
Port D Bit 7, Red LED
Port E Bit 0, Red LED
26
Port D Bit 5, Green LED
Port D Bit 0, Green LED
27
Port D Bit 4, OutputCapture pin
Port D Bit 1, OutputCapture pin
Vcc
Power, common with pin 21
Power, common with pin 21
Reset
Reset, common with pin 22
Reset, common with pin 22
SCK
SPI Clock
SPI Clock
MISO
SPI Master In Slave Out
SPI Master In Slave Out
MOSI
SPI Master Out Slave In
SPI Master Out Slave In
Gnd
Ground, common with pins 4 and 23
Ground, common with pins 4 and 23
CS
On-board EEPROM Chip Select or
Slave Select for SPI
Slave Select for SPI
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