PORT A TIMING
MOTOROLA
PORT A
4 - 9
and Y: memory spaces. Although external program memory must be 24 bits, external data
memory does not. Of course, this is application specific. Many systems use 16 or fewer bits
for A/D and D/A conversion and, therefore, they may only need to store 16, 12, or even eight
bits of data. The 24/56 bits of internal precision is usually sufficient for intermediate results.
This is a cost saving feature which can reduce the number of external memory chips.
4.3
PORT A TIMING
The external bus timing is defined by the operation of the address bus, data bus, and bus
control pins. The transfer of data over the external data bus is synchronous with the clock.
The timing A, B, and C relative to the edges of an external clock (see Figure 4-6 and Fig-
ure 4-7) are provided in the
DSP56002 Advance Information Data Sheet (DSP56002/D)
.
This timing is essential for designing synchronous multiprocessor systems. Figure 4-6
shows the port A timing with no wait states (wait-state control is discussed in Section 4.4).
One instruction cycle equals two clock cycles or four clock phases. The clock phases,
which are numbered T0 – T3, are used for timing on the DSP. Figure 4-7
shows the same
timing with two wait states added to the external X: memory access.
Four TW clock phases have been added because one wait state adds two T phases and
T0
T1
T2
T3
T0
T1
T2
T3
T0
T1
ONE INSTRUCTION CYCLE
ONE CLOCK CYCLE
INTERNAL CLOCK PHASES
ADDRESS PS, DS, X/Y
A
B
C
RD
DATA IN
WR
DATA OUT
READ
CYCLE
WRITE
CYCLE
Figure 4-6 Port A Bus Operation with No Wait States
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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