The LS7166 is a CMOS, 24-bit counter that can be programmed to operate in several different modes. The operating mode is set up by writing control words into internal control registers (see Figure 8). There are three 6-bit and one 2-bit control registers for setting up the circuit functional characteristics. In addition to the control registers, there is a 5-bit output status register (OSR) that indicates the current counter status. The IC communicates with external circuits through an 8-bit three state I/O bus. Control and data words are written into the LS7166 through the bus. In addition to the I/O bus, there are a number of discrete inputs and outputs to facilitate instantaneous hardware based control functions and instantaneous status indication.