Motorola MPC8240, Руководство пользователя

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Chapter 4. Configuration Registers 4-53
Memory Control Configuration Registers
20 BUF_TYPE[1] 0 Least significant bit of the memory data bus buffer type field. BUF_TYPE[1] is
used with bit 22 above (BUF_TYPE[0]) to configure the internal memory data
path buffering scheme as described for bit 22.
19–18 BSTOPRE[0–1] 00 Burst to precharge—bits 0–1. For SDRAM only. These bits, together with
BSTOPRE[2–5] (bits 31–28 of MCCR3), and BSTOPRE[6–9] (bits 3–0 of
MCCR4), control the open page interval. The page open duration counter is
reloaded with BSTOPRE[0–9] every time the page is accessed (including page
hits). When the counter expires, the open page is closed with a
SDRAM-precharge bank command. See Chapter 6, “MPC8240 Memory
Interface,” for more information.
17–16 — 00 Reserved
15 REGDIMM 0 Registered DIMMs. Memory data and parity data path buses configured for
registered DIMMs. For SDRAM only. When enabled (REGDIMM = 1), SDRAM
write data and parity are delayed by one cycle on the memory bus with respect
to the SDRAM control signals (for example, SDRAS, SDCAS, WE).
0 Normal DIMMs
1 Registered DIMMs selected
14–8 SDMODE All 0s SDRAM mode register. For SDRAM only. These bits specify the SDRAM mode
register data to be written to the SDRAM array during power-up configuration.
Note that the SDRAM mode register ‘opcode’ field is not specified and is forced
to b’0_0000’ by the MPC8240 when the mode registers are written.
Bits 14–12 CAS latency
000 Reserved
001 1
010 2
011 3
100 Reserved
101 Reserved
110 Reserved
111 Reserved
Bit 11 Wrap type
0 Sequential. Default for MPC8240
1 Interleaved - Reserved
Bits 10–8 Burst length
000 Reserved
001 Reserved
010 4
011 8
100 Reserved
101 Reserved
110 Reserved
111 Reserved
Table 4-41. Bit Settings for MCCR4—0xFC (Continued)
Bits Name
Reset
Value
Description