Data Acquisition

This is the data register of the first timer/counter.Before reading or writing from this register, a control word for this counter must bewritten to the timer/counter control register. Then ‘reads’ and ‘writes’ to this registermust follow the format specified in the control word. Figure D.4TC0 registerThe bits TC0 7 (MSB) down to TC0 0 (LSB) reflect the high byte or the low byte of the data‘read from’ or ‘written to’ this counter.This register is the data register of the second timer/counter.Before reading or writing from this register, a control word for this counter must bewritten to the timer/counter control register. Then ‘reads from’ and ‘writes to’ thisregister must follow the format specified in the control word. Figure D.5TCI registerThe bits TC1 7 (MSB) down to TC1 0 (LSB) reflect the high byte or the low byte of the dataread or written to this counter.This register is the data register of the third timer/counter.Before reading or writing from this register, a control word for this counter must be‘written to’ the timer/counter control register. Then ‘reads from’ and ‘writes to’ thisregister must follow the format specified in the control word. Figure D.6TC2 registerThe bits TC2 7 (MSB) down to TC2 0 (LSB) reflect the high byte or the low byte of thedata read or written to this counter.D.3 Programming a counterOn power-up or reset, the state of the 8254 is undefined. Before any timer/counteroperations can be performed, each timer to be used must be programmed with a controlword, which is written to the control register. This sets the individual counters:• Operating mode (Mode 0 to 5)