Data Acquisition

• Counting format (BCD or binary)• Read/write format (LSB only, MSB only or LSB then MSB)The programmed counter then operates in the specified format until it is reset or newconfiguration information is written to the control register. The format of this registerwhen used for configuring a counter is repeated below for reference.Figure D.7TCCTRL register – configuration modeUsing the control word, each counter may be programmed to transfer data from the hostcomputer in one of three ways:• Read/write least significant byte only• Read/write most significant byte only or• Read/write least significant byte first, then most significant byteA new initial count may be written to a counter without affecting the counter’sprogramming in any way. Counting will be affected as described in the mode definitionsbelow.Writing a 1-byte initial count simply consists of outputting the byte to the counter’sdata register. Writing a 2-byte count consists of writing the first byte (the least significantbyte) to the counter’s data register and then, at any time later, writing the second or mostsignificant byte to the same data register.The clock pulse input is the physical connection, where clock pulses are applied to acounter. A clock pulse is defined as a rising edge, then a falling edge, in that order, at acounter’s clock input. New counts are loaded, and the counting element is decremented,on the falling edge of a clock pulse.Depending on the counter’s mode, the gate input provides for enable/disable counting,count initiating (trigger), or setting/resetting the timer output.D.4 Read operationsIt is often necessary to read the value or status of a counter without disturbing the count inprogress. There are three methods: