mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 375

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

15.3.1.5 MACHINE A MODE REGISTER. The machine A mode register (MAMR) contains
the configuration for the user-programmable machine A. See Figure 15-1 (page 15-3) for
more information.
PTA—Periodic Timer A Period
This field affects the periodic timer A and determines the timer period service rate using the
following equation:
NCS is an integer between 1 and 8 that represents the number of enabled chip-selects that
select this UPM. The DFBRG field is the division factor for the BRGCLK, which can be
divided by 1 (default), 4, 16, or 64 and is programmed in the SCCR (described in
Section 5.2.1 System Clock and Reset Control Register).
For example, for DRAM to maintain data integrity an access or refresh must occur every
15.6 s. Use the equation above to determine the PTA value for UPMA to perform memory
refresh. Given that you have a 25MHz system clock with the required service rate of 15.6 s,
a periodic timer prescaler equal to 32, and a DFBRG field that is equal to 0, then the PTA
value must be (25 15.6) / (2
per service, use the TLFA field.
MAMR
PTA
RESET
RESET
FIELD
ADDR
FIELD
ADDR
R/W
R/W
BIT
BIT
=
System Clock (MHz) Service Duration (µs)
-------------------------------------------------------------------------------------------------------------------- -
16
0
2
Note: The UPM refresh is done in a round robin manner. If more than one chip-select
G0CLA
2 DFBRG
R/W
17
1
0
18
uses the same UPM, the refreshes will progress through each one. For example,
if you have three chip-selects using UPMA, you would need to set the periodic
timer A period to one-third the normal refresh.
2
Freescale Semiconductor, Inc.
Prescaler (PTP) NCS
GPLA4
For More Information On This Product,
R/W
19
DIS
3
1
PTA
R/W
2 0
0
20
MPC823 REFERENCE MANUAL
4
32 1) = 12. If you want to perform more than one refresh
Go to: www.freescale.com
21
5
RLFA
R/W
0
22
6
(IMMR & 0xFFFF0000) + 0x170
(IMMR & 0xFFFF0000) + 0x172
23
7
PTAE
R/W
24
8
0
25
9
WLFA
R/W
0
AMA
R/W
10
26
0
11
27
RES
R/W
12
28
0
Memory Controller
13
29
TLFA
DSA
R/W
R/W
0
0
14
30
15-19
RES
R/W
15
31
0