CTC General Description
   The Z80 CTC is a four-channel counter/timer that can be programmed by system software for a broad range of counting and timing applications.
   These four independently programmable channels satisfy common microcomputer system requirements for event counting, interrupt and interval timing, and general clock rate generation. 
   System design is simplified by connecting the CTC directly to both the Z80 CPU and the Z80 SIO with no additional logic. In larger systems, address decoders and buffers may be required.

CTC FEATURES
• Four independently programmable counter/timer channels (CTC),
   each with a readable down-counter and a selectable 16 or 256
   prescaler. Down-counters are reloaded automatically at zero count
• Selectable positive or negative trigger initiates timer operation
• Three channels have zero count/timeout outputs capable of driving
   Darlington transistors
• NMOS version for high-cost performance solutions
• CMOS version for the designs requiring low power consumption
• NMOS Z0843004 - 4 MHz, Z0843006 - 6.17 MHz
• CMOS Z84C3006 - dc to 6.17 MHz, Z84C3008 dc to 8 MHz,
   Z84C3010 - dc to 10 MHz
• Interfaces directly to the Z80 CPU. Interfaces to the Z80 SIO for baud
   rate generation
• Standard Z80 Family daisy-chain interrupt structure provides fully
   vectored, prioritized interrupts without external logic. The CTC may
   also be used as an interrupt controller
• A 6 MHz version supports 6.144 MHz CPU clock operation