Embedded Systems Design, 2nd Edition

50 Embedded systems design

The M68000 upper and lower data strobes have been re-

placed by A0 and the two size pins, SIZE0 and SIZE1. These

indicate the amount of data left to transfer on the current bus cycle

and, when used with address bits A0 and A1, can provide decode

information so that the correct bytes within the 4 byte wide data

bus can be enabled. The old DTACK* signal has been replaced by

two new ones, DSACK0* and DSACK1*. They provide the old

DTACK* function of indicating a successful bus cycle and are used

in the dynamic bus sizing. The bus interface is asynchronous and

similar to the M68000 cycle but with a shorter three–cycle se-

quence, ...