Keithley PIO-12 User Manual page 22

P10-12 programmability is provided through the board's 8255
Programmable Peripheral Interface (PPI) integrated circuit. The 8255 PPI
provides 24 digital I/O lines, which make up the following three ports:
• P O R T A (abbreviated PA) consists of one 8-bit data output
latch/buffer and one 8-bit data input latch.
• P O R T B (PB) consists of one 8-bit data output latch/buffer and one
8-bit data input buffer.
• P O R T C (PC) consists of one 8-bit data output latch/buffer and one
8-bit data input buffer. This port can also be used as two 4-bit ports:
PC Upper (PC4 to PC7) and PC Lower (PCO to PC3).
Programming the PIO-12 involves two fundamental tasks: setting the port
configuration and reading/writing data from/to the ports. These tasks are
discussed in the sections that follow.
Note: I f you need more detailed information on the 8255 PPI, please
contact an Intel representative for a complete data sheet on the 8255 PPI.
Programming
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