Navigation bar
  Start Previous page
 140 of 156 
Next page End 135 136 137 138 139 140 141 142 143 144 145  

134
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
The first alternate above is similar to the circuitry used on the ZX-24 series devices.  The advantage to
this circuit is its simplicity.  The disadvantage is that the voltage levels of the serial output signal do not
meet the RS-232 standard.  Even so, most serial receivers are able to properly interpret the output signal. 
Note that if the inverters used have protection diodes on their inputs the external diodes shown are not
necessary.
The second alternate serial interface is shown in the diagram below.  This circuit produces a serial output
signal that meets the RS-232 standard by using the negative voltage on the receive line to provide a
reference for the output level.  Although the parts count is higher, the circuit uses inexpensive and non-
critical components.
Alternate Serial Interface Circuit #2
Previous page Top Next page