Rabbit Rabbit 4000, User Manual

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56 Rabbit 4000 Microprocessor User’s Manual
MMU Expanded Code Register (MECR) (Address = 0x0018)
Bit(s) Value Description
7:5 000 Bank select address is A[19:18].
001 Bank select address is A[20:19].
010 Bank select address is A[21:20].
011 Bank select address is A[22:21].
100 Bank select address is A[23:22].
101 This bit combination is reserved and should not be used.
110 This bit combination is reserved and should not be used.
111 Bank select address is A[18:17].
4:3 These bits are reserved and should be written with zeros. Read returns zeros.
2:0 000 Normal operation.
001 This bit combination is reserved and should not be used.
010 This bit combination is reserved and should not be used.
011 This bit combination is reserved and should not be used.
100 For an XPC access, use MB0CR independent of bank select address.
101 For an XPC access, use MB1CR independent of bank select address.
110 For an XPC access, use MB2CR independent of bank select address.
111 For an XPC access, use MB3CR independent of bank select address.
Memory Timing Control Register (MTCR) (Address = 0x0019)
Bit(s) Value Description
7:4 These bits are reserved and should be written with zeros.
3 0 Normal timing for /OE1 (rising edge to rising edge, one clock minimum).
1 Extended timing for /OE1 (one-half clock earlier than normal).
2 0 Normal timing for /OE0 (rising edge to rising edge, one clock minimum).
1 Extended timing for /OE0 (one-half clock earlier than normal).
1 0
Normal timing for /WE1 (rising edge to falling edge, one and one-half clocks
minimum).
1 Extended timing for /WE1 (falling edge to falling edge, two clocks minimum).
0 0
Normal timing for /WE0 (rising edge to falling edge, one and one-half clocks
minimum).
1 Extended timing for /WE0 (falling edge to falling edge, two clocks minimum).