The Intersil ACS161MS is a Radiation Hardened 4-Bit Binary Synchronous Counter. The MR is an active low master reset. SPE is an active low Synchronous Parallel Enable which disables counting and allows data at the preset inputs (P0 - P3) to load the counter. CP is the positive edge clock. TC is the terminal count or carry output. Both TE and PE must be high for counting to occur, but are irrelevant to loading. TE low will keep TC low.