Data Acquisition

The bits A7 (MSB) down to A0 (LSB) reflect the status of the port’s I/O lines.Depending on the programmed I/O mode of the port, the lines may be inputs, outputs orbi-directional.C.3 DIOB – port B of the 8255 (offset 1, read/write)This register is the data register of port B of the 8255. The port can be operated in simpleI/O mode or strobed I/O mode, modes 0, or 1. Figure C.4Port B of the 8255The bits B7 (MSB) down to B0 (LSB) reflect the status of the port’s I/O lines.Depending on the programmed I/O mode of the port, the lines may be inputs or outputs.C.4 DIOC – port C of the 8255 (offset 2, read/write)This register is port C of the 8255. It may operate in simple I/O mode, or some or all ofits lines may be used as handshaking control lines for ports A and B when these portsoperate in mode 1 or 2 and are therefore not available as I/O lines. It is more meaningfulto refer to them by their functional names, summarized in the following table anddescribed below that. Figure C.5Port C of the 8255The bits C7 (MSB) down to C0 (LSB) reflect the status of the port’s available I/O lines.Depending on the programmed 1/0 mode of the port, the lines may be inputs or outputs.The other lines may be handshakes or interrupt request lines. Table C.4Port C line usage