Programmable bank switching, 5 programmable bank switching – Texas Instruments TMS320C3x User Manual
Page 278
Programmable Bank Switching
9-12
9.5
Programmable Bank Switching
Programmable bank switching allows you to switch between external memory
banks without having to insert wait states externally due to memories that require
several cycles to turn off. Bank switching is implemented on the primary bus only.
The size of a bank is determined by the number of bits specified by the BNKCMP
field of the primary bus control register. For example, if BNKCMP = 16, the 16
MSBs of the address are used to define a bank (see Figure 9–4). Since
addresses are 24 bits, the bank size is specified by the eight LSBs, yielding a
bank size of 256 words. If BNKCMP
≥
16, only the 16 MSBs are compared. Bank
sizes from 2
8
= 256 to 2
24
= 16M are allowed. Table 9–6 summarizes the relation-
ship between BNKCMP, the address bits used to define a bank, and the resulting
bank size.
Figure 9–4. BNKCMP Example
23
8
7
0
24-bit address
Number of bits to compare
Defines bank size
Table 9–6. BNKCMP and Bank Size
BNKCMP
MSBs Defining a Bank
Bank Size (32-Bit Words)
00000
None
2
24 =
16M
00001
23
2
23
= 8M
00010
23–22
2
22
= 4M
00011
23–21
2
21
= 2M
00100
23–20
2
20
= 1M
00101
23–19
2
19
= 512K
00110
23–18
2
18
= 256K
00111
23–17
2
17
= 128K
01000
23–16
2
16
= 64K
01001
23–15
2
15
= 32K
01010
23–14
2
14
= 16K
01011
23–13
2
13
= 8K
01100
23–12
2
12
= 4K
01101
23–11
2
11
= 2K
01110
23–10
2
10
= 1K
01111
23–9
2
9
= 512
10000
23–8
2
8
= 256
10001–11111
Reserved
Undefined