TMS320VC5420
FIXED-POINT DIGITAL SIGNAL PROCESSOR
SPRS080C – MARCH 1999 – REVISED APRIL 2000
programmable bank-switching
Programmable bank-switching can be used to insert one cycle automatically when crossing memory-bank
boundaries inside program memory or data memory space. One cycle can also be inserted when crossing from
program-memory space to data-memory space (’54x) or one program memory page to another program
memory page. This extra cycle allows memory devices to release the bus before other devices start driving the
bus; thereby avoiding bus contention. The size of the memory bank for the bank-switching is defined by the
bank-switching control register (BSCR). The BSCR of a particular DSP subsystem (A or B) is used for the
external memory interface depending on the logic level of the SELA/B pin.
15
12
11
10
9
8
7
3
2
1
0
BNKCMP
R/W
PS-DS
R/W
Reserved
R/W
IPIRQ
R/W
Reserved
BH
R/W
Reserved
EXIO
R/W
LEGEND: R = Read, W = Write
Figure 5. BSCR Register Bit Layout for Each DSP Subsystem
Table 4. BSCR Register Bit Functions for Each DSP Subsystem
BIT
NO.
BIT
NAME
RESET
VALUE
FUNCTION
Bank compare. BNKCMP determines the external memory-bank size. BNKCMP is used to mask the four
MSBs of an address. For example, if BNKCMP = 1111b, the four MSBs (bits 12–15) are compared,
resulting in a bank size of 4K words. Bank sizes of 4K words to 64K words are allowed.
15–12
11
BNKCMP
PS-DS
1111
Program read – data read access. PS-DS inserts an extra cycle between consecutive accesses of
program read and data read or data read and program read.
1
PS-DS = 0
PS-DS = 1
No extra cycles are inserted by this feature.
One extra cycle is inserted between consecutive data and program reads.
10–9
8
Reserved
IPIRQ
0
0
0
These bits are reserved and are unaffected by writes.
The IPIRQ bit is used to send an interprocessor interrupt to the other subsystem. IPIRQ=1 sends the
interrupt.IPIRQmustbeclearedbeforesubsequentinterruptscanbemade. Refertotheinterruptssection
for more details
7–3
Reserved
These bits are reserved and are unaffected by writes.
Bus holder. BH controls the data bus holder feature: BH is cleared to 0 at reset.
BH = 0
BH = 1
The bus holder is disabled.
The bus holder is enabled. When not driven, the data bus (PPD[15:0]) is held in the
previous logic level.
2
1
BH
0
0
Reserved
These bits are reserved and are unaffected by writes.
External bus interface off. The EXIO bit controls the external bus-off function.
EXIO = 0
EXIO = 1
The external bus interface functions as usual.
The address bus, data bus, and control signals become inactive after completing the
current bus cycle. Note that the DROM, MP/MC, and OVLY bits in the PMST and the
HM bit of ST1 cannot be modified when the interface is disabled.
0
EXIO
0
22
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