Motorola M6800 manual THREE-STATE Control TSC, Address BUS AO/A15

MPU-11

available. This will occur if the GO/HALT line is in the Halt (low) mode or the 14PU is in a "Wait" state as the result of some instruction, such as the WAI instruction.

10.THREE-STATE CONTROL: (TSC)

This input causes all of the address lines and the Read/Write line to go into the off or high impedance state. The Valid Memory address and Bus Available signals will be forced low. The data bus is not affected by TSC and has its own enable (Data Bus Enable). In DMA applications, the Three-State Control line should be brought high on the leading edge of the Phase One Clock. The 11 clock must be held in the high state for this function to operate properly. The address bus will then be available for other devices to directly address memory. Since the MPU is a dynamic device, it must be refreshed periodically or destruction of data will occur.

11.ADDRESS BUS (AO/A15):

Sixteen pins are used for the address bus. The outputs are three-state bus drivers capable of driving one standard TTL load and 130pf at 1 Megahertz.

When the output is turned off, it is essentially an open circuit. This permits the MPU to be used in DMA applications.

12.DATA BUS (DO/D7):

Eight pins are used for the data bus. It is bi-directional, transferring data to and from the memory and peripheral devices. It also has three-state output buffers capable of driving one standard TTL load and 130pf at 1 Megahertz.