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Bus Interface Unit (BIU) Registers
4
-28
DSP56303 User’s Manual
Figure 4-7. DRAM Control Register (DCR)
Table 4-9. DRAM Control Register (DCR) Bit Definitions
Bit
Number
Bit Name
Reset
Value
Description
23 BRP
0
Bus Refresh Prescaler
Controls a prescaler in series with the refresh clock divider. If BPR is set, a
divide-by-64 prescaler is connected in series with the refresh clock divider. If BPR is
cleared, the prescaler is bypassed. The refresh request rate (in clock cycles) is the
value written to BRF[7–0] bits + 1, multiplied by 64 (if BRP is set) or by one (if BRP is
cleared). When programming the periodic refresh rate, you must consider the RAS
time-out period. Hardware support for the RAS time-out restriction does not exist
.
NOTE: Refresh requests are not accumulated and, therefore, in a fast refresh request
rate not all the refresh requests are served (for example, the combination BRF[7–0] =
$00 and BRP = 0 generates a refresh request every clock cycle, but a refresh access
takes at least five clock cycles).
22–15
BRF[7–0]
0
Bus Refresh Rate
Controls the refresh request rate. The BRF[7–0] bits specify a divide rate of 1–256
(BRF[7–0] = $00–$FF). A refresh request is generated each time the refresh counter
reaches zero if the refresh counter is enabled (BRE = 1).
14
BSTR
0
Bus Software Triggered Reset
Generates a software-triggered refresh request. When BSTR is set, a refresh request
is generated and a refresh access is executed to all DRAM banks (the exact timing of
the refresh access depends on the pending external accesses and the status of the
BME bit). After the refresh access (CAS before RAS) is executed, the DRAM controller
hardware clears the BSTR bit. The refresh cycle length depends on the BRW[1–0] bits
(a refresh access is as long as the out-of-page access).
13
BREN
0
Bus Refresh Enable
Enables/disables the internal refresh counter. When BREN is set, the refresh counter is
enabled and a refresh request (CAS before RAS) is generated each time the refresh
counter reaches zero. A refresh cycle occurs for all DRAM banks together (that is, all
pins that are defined as RAS are asserted together). When this bit is cleared, the
refresh counter is disabled and a refresh request may be software triggered by using
the BSTR bit. In a system in which DSPs share the same DRAM, the DRAM controller
of more than one DSP may be active, but it is recommended that only one DSP have
its BREN bit set and that bus mastership is requested for a refresh access. If BREN is
set and a WAIT instruction is executed, periodic refresh is still generated each time the
refresh counter reaches zero. If BREN is set and a STOP instruction is executed,
periodic refresh is not generated and the refresh counter is disabled. The contents of
the DRAM are lost.
23
22
21
20
19
18
17
16
15
14
13
12
BRP
BRF7
BRF6
BRF5
BRF4
BRF3
BRF2
BRF1
BRF0
BSTR
BREN
BME
11
10
9
8
7
6
5
4
3
2
1
0
BPLE
BPS1
BPS0
BRW1
BRW0
BCW1
BCW0
Reserved bit. Read as zero; write to zero for future compatibility
Содержание DSP56303
Страница 1: ...DSP56303 User s Manual 24 Bit Digital Signal Processor DSP56303UM AD Revision 1 January 2001 ...
Страница 52: ...JTAG OnCE Interface 2 22 DSP56303 User s Manual ...
Страница 114: ...General Purpose Input Output GPIO 5 10 DSP56303 User s Manual ...
Страница 212: ...GPIO Signals and Registers 8 26 DSP56303 User s Manual ...
Страница 268: ...Interrupt Equates A 22 DSP56303 User s Manual ...
Страница 306: ...Programming Sheets B 38 DSP56303 User s Manual ...
Страница 320: ...Index 14 DSP56303 User s Manual ...