Freescale Semiconductor PowerQUICC MPC870, Справочное руководство

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Memory Controller
MPC885 PowerQUICC Family Reference Manual, Rev. 2
15-12 Freescale Semiconductor
These registers are affected by HRESET but are not affected by SRESET. Figure 15-4 describes ORx
fields.
Table 15-4. OR x Field Descriptions
Bits Name Description
0–16 AM Address mask. This read/write field independently masks bits A[0:16] on the address bus so
external devices of different size address ranges can be used. AM bits can be set or cleared in any
order, allowing a resource to reside in more than one area of the address map.
0 The corresponding address bit is masked.
1 The corresponding address bit is used in address pin comparison.
17–19 ATM Address type mask. Masks certain bits in address type, AT[0:2], allowing more than one address
space type to be assigned to a chip-select. Any set bit causes the corresponding address type code
bits to be used as part of the address comparison. Any cleared bit masks the corresponding address
type code bit. If address-type protection is not desired, ATM should be cleared.
20 CSNT CSNT (chip-select negation time). Used for the GPCM with ACS and TRLX to control negation of
CSx and WEx during an external memory write access. Provides extended address/data hold time
for slower memories and peripherals. This will not be applicable when SETA = 1. See
Table 15-11 .
SAM Start address multiplex. Used for a UPM to determine the address output on the first cycle of an
external memory access. Should be set only if address multiplexing is to be performed internally.
0 Address pins are not multiplexed internally.
1 Address pins reflect the address requested by the internal master multiplexed according to the
setting of MAMR[AMA] (UPMA) or MBMR[AMB] (UPMB).
21–22 ACS ACS (address to chip-select setup). Lets the GPCM control CSx assertion relative to address lines
valid.
00 CS is output at the same time as the address lines.
01 Reserved.
10 CS is output a quarter of a clock after the address lines.
11 CS is output half a clock after the address lines.
G5LA,
G5LS
G5LA and G5LS (general-purpose line 5 A/line 5 start) are used for the UPM to determine how the
internal controls and timing generator signal outputs GPL5 when a UPM handles a memory access.
G5LA (valid only for UPMB):
0 Output the internal GPL5 signal on GPL_B5.
1 Output the internal GPL5 signal on GPL_A5.
G5LS (valid for UPMA or UPMB)
0 GPL5 is driven low on the falling edge of GCLK1_50 in the first clock cycle of a memory access.
1 GPL5 is driven high on the falling edge of GCLK1_50 in the first clock cycle of a memory access.
23 BIH Burst inhibit. Determines whether this memory bank supports burst accesses. If the machine
selected to handle this access is the GPCM, BIH must be set.
0 BI is negated. The bank supports burst accesses.
1 BI is asserted. The bank does not support burst accesses.
24–27 SCY Select cycle length (GPCM only). Binary representation of the number of wait states inserted in the
cycle when the GPCM handles an external memory access (0000 = 0 clock cycle, 0001 = 1 clock
cycle, …, 1111 = 15 clock cycle). Total cycle length is also affected by TRLX. See
Table 15-11 for
the total number of cycles. If external TA response is selected (SETA = 1), SCY is not used.
28 SETA Select external transfer acknowledge (GPCM only).
0 Internal or external transfer acknowledge can acknowledge this access, whichever comes first.
1 The memory controller does not generate TA for this bank; instead the peripheral must generate
it on the external TA signal.