Texas Instruments TMS320C3x - Manual (Page 335)

8-Bit-Wide Memory Interface
10-32
10.8 8-Bit-Wide Memory Interface
’C32 memory interface to an 8-bit wide external memory uses STRBx_B3 and
STRBx_B2 pins as additional address pins, A
–1
and A
–2
, respectively, while
using STRBx_B0 as strobe byte-enable pin as shown in Figure 10–18. The
external-memory address pins are connected to the ’C32’s address pins
A
21
A
20
...A
1
A
0
A
–1
A
–2
. In this manner, the ’C32 can read/write a single 32-, 16-,
or 8-bit value from the external 8-bit-wide memory.
Figure 10–18. External Memory Interface for 8-Bit SRAMs
A
23
A
22
A
21
.
.
A
1
A
0
STRBx_B2/A
–2
R/W
A23
.
.
A3
A2
A0
WE
CS
I/O(7- 0)
’C32
STRBx_B1
STRBx_B0
D(31-24)
D(23-16)
D(15-8)
D(7-0)
STRBx_B3/A
–1 A1
Case 7: 8-Bit-Wide Memory With 8-Bit Data-Type Size
Similarly to case 4, the ’C32 shifts the internal address two bits to the right
before presenting it to the external-address pins when the data type is 8-bit. As
in case 4, the memory interface copies the value of the internal-address A
23
to
the external-address pins A
23
, A
22
, and A
21
. But in case 7, the memory interface
also copies the value of the internal-address A
1
to the external STRBx_B3/A
–1
pin and the value of A
0
to the external STRBx_B2/A
–2
. Moreover, the memory
interface only activates the STRBx_B0 pin during the external memory access.
Figure 10–19 shows a functional diagram of the memory interface for 8-bit-wide
memory with an 8-bit data-type size.