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PARALLEL PROGRAMMING INTERFACE
Another feature of the parallel interface connector is that of a parallel interface that allows for
programming. In this mode of operation a character buffer of 32 characters is provided for the
user. The characters are designated as
∅
through 31 (see Figure 37).
These 32 characters can be pre-programmed via serial commands to represent distance, velocity
(in RPM only), count, etc. The same basic functions and programming capabilities that are
provided for thumbwheels are provided for this parallel interface.
The parallel interface has 8 lines dedicated to transfer data and 4 lines dedicated to selection of
data pairs.
Since 8 lines of data are provided, each data transfer includes two characters. The additional 4
lines allow for a selection of 16 pairs of characters.
The operation of the data lines is for BCD data. The 4 lines of pair selections are coded in
binary.
Four handshake lines are dedicated to accomplish data transfers. Two are inputs and two are
outputs. One input (PAIR ENTER) is to tell the digital drive that the data and pair selection lines
are ready for transferring to the character buffer. Once the 32-character buffer data content is
programmed, another input (EXECUTE) is provided to transfer and start using any new data
contained in the entire buffer.
One of the outputs (ACKNOWLEDGE) is provided as a means for the digital drive to tell the
external device that it has received the proper input. This output comes ON to acknowledge
either of the inputs. (PAIR ENTER) or (EXECUTE).
The second output is called (ERROR) and is provided as a means for the drive to tell an external
device that data is out of range. The correct protocol for these handshake lines is to turn on the
input, wait for the acknowledge and then shut off the input. The digital drive will than shut off
(ACKNOWLEDGE).
The inputs and outputs from this parallel interface are not optically isolated and are relatively
low voltage (5 to 15). Care must be taken to assure that electrical noise does not enter the digital
drive by a careless wiring implementation of this interface. In general, the wiring should be kept
short (5 to 20 feet). The wiring should be shielded with the shield connected at the external
device. The wiring cannot be run adjacent to any high voltage wiring.
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