ZBasic Language Reference
221
ZBasic Microcontrollers
Recommended Serial Interface Circuit
The pullup resistor shown on the AVR’s transmit output (TxD) is needed to ensure that the serial output
line stays in the idle state during reset cycles. Its value is non-critical – anything from 4.7K to 22K should
work fine. The pullup resistor on the reset input isn’t technically required since the chip itself has an
internal pullup. The external pullup could be eliminated or could be made larger if desired.
There are other serial interface circuits that would provide the required functionality, two of which are
shown below. Both alternate circuits use the same ATN circuitry as the recommended circuit above.
Alternate Serial Interface Circuit #1
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