Memory Controller
MPC885 PowerQUICC Family Reference Manual, Rev. 2
15-14
Freescale Semiconductor
15.4.4
Machine A Mode Register/Machine B Mode Registers
(M
x
MR)
The machine x mode register (MAMR and MBMR) contain the configuration for UPMA and UPMB,
respectively. See
Figure 15-1
.
This register is affected by HRESET but is not affected by SRESET.
Table 15-6
describes bits for
MAMR/MBMR.
0
7
8
9
10
11
12
13
14
15
Field
PT
x
PT
xE
AM
x
—
DS
x
—
Reset
xxxx_xxxx_0000_0000
R/W
R/W
Addr
(IMMR & 0xFFFF0000) + 0x170
16
17
18
19
20
23
24
27
28
31
Field
G0CL
x
GPL
x4DIS
RLF
x
WLF
x
TLF
x
Reset
000
1
0000
0000
0000
R/W
R/W
Addr
(IMMR & 0xFFFF0000) + 0x172
Figure 15-10. Machine A Mode Register/Machine B Mode Register (M
x
MR)
Table 15-6. M
x
MR Field Descriptions
Bits
Name Description
0–7
PT
x
Periodic timer
x period. Affects periodic timer x and determines the timer period service rate
according to the following equation, which determines value for UPM
x to refresh memory:
NCS is an integer between 1 and 8 that represents the number of enabled chip selects that
are serviced by this UPM. SCCR[DFBRG] is defined in
Section 14.6.1, “System Clock and
Reset Control Register (SCCR).”
For example, for DRAM to maintain data integrity, an
access or refresh must occur every 15.6 µs. Given a 25-MHz system clock with the required
service rate of 15.6µs, a periodic timer prescaler = 32, and DFBRG = 0, PT
x = (25 x 15.6)
/ (2
2
x
0
x 32x 1) = 12.
8
PT
xE
Periodic timer
x enable. Allows the periodic timer x to request service.
0 Periodic timer
x is disabled.
1 Periodic timer
x is enabled.
9–11
AM
x
Address multiplex size
x. When internal address multiplexing is used, this field specifies how
the address on the external bus is multiplexed, when enabled (see
Table 15-18
). The SAM
bit enables address multiplexing in the first clock cycle. The AM
x field of the RAM array entry
enables address multiplexing in subsequent clock cycles. (see
Table 15-19
).
12
—
Reserved, should be cleared.
PTx
System Clock (MHz)
Service Duration (µs)
×
2
2
S CC R DF B RG
[
]
×
Prescaler (PTP)
×
NCS
×
---------------------------------------------------------------------------------------------------------------------
=
Содержание PowerQUICC MPC870
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