Data Acquisition

Table C.6Instructions for reading or writing to the portsC.5 Mode 0: simple I/OThis mode is used for simple input and output operations for each of the ports. Nohandshaking is required and no interrupts are generated. Data is simply read from orwritten to a selected port.The following characterize mode 0:• Two 8-bit ports (ports A and B) and two 4-bit ports (upper and lower nibbleof port C)• Any port can be configured for input or output• Outputs are latched, inputs are not latched• Data transfer by polled I/OC.6 Mode 0 programmingTo use the 8255 in mode 0:• Write a single byte to the control register to set the 8255 into mode 0 with thethree ports configured for the desired data direction• Then read to or write from the I/O port corresponding to an 8255 port (port A,B or C) as many times as necessary to obtain or transfer the required amountof dataC.7 Mode 1: strobed I/OIn this mode data transfers are controlled by handshaking signals and hardware interrupts.Some of the port C lines are used for these control signals. Hence they take on differentfunctions and names. The following characterize Mode 1:• Two groups, group A and B. Each group consists of an 8-bit data port andthree control lines• Certain port C lines take on special functions• The data ports can be either input or output ports