C8051F120/1/2/3/4/5/6/7
206
Rev. 1.2
18.6. Timing
The timing parameters of the External Memory Interface can be configured to enable connection to devices having
different setup and hold time requirements. The Address Setup time, Address Hold time, /RD and /WR strobe widths,
and in multiplexed mode, the width of the ALE pulse are all programmable in units of SYSCLK periods through
EMI0TC, shown in Figure 18.6, and EMI0CF[1:0].
The timing for an off-chip MOVX instruction can be calculated by adding 4 SYSCLK cycles to the timing parameters
defined by the EMI0TC register. Assuming non-multiplexed operation, the minimum execution time for an off-chip
XRAM operation is 5 SYSCLK cycles (1 SYSCLK for /RD or /WR pulse + 4 SYSCLKs). For multiplexed opera-
tions, the Address Latch Enable signal will require a minimum of 2 additional SYSCLK cycles. Therefore, the mini-
mum execution time for an off-chip XRAM operation in multiplexed mode is 7 SYSCLK cycles (2 for /ALE + 1 for
/RD or /WR + 4). The programmable setup and hold times default to the maximum delay settings after a reset.
Table 18.1 lists the AC parameters for the External Memory Interface, and Figure 18.7 through Figure 18.12 show the
timing diagrams for the different External Memory Interface modes and MOVX operations.
Figure 18.6. EMI0TC: External Memory Timing Control
Bits7-6:
EAS1-0: EMIF Address Setup Time Bits.
00: Address setup time = 0 SYSCLK cycles.
01: Address setup time = 1 SYSCLK cycle.
10: Address setup time = 2 SYSCLK cycles.
11: Address setup time = 3 SYSCLK cycles.
Bits5-2:
EWR3-0: EMIF /WR and /RD Pulse-Width Control Bits.
0000: /WR and /RD pulse width = 1 SYSCLK cycle.
0001: /WR and /RD pulse width = 2 SYSCLK cycles.
0010: /WR and /RD pulse width = 3 SYSCLK cycles.
0011: /WR and /RD pulse width = 4 SYSCLK cycles.
0100: /WR and /RD pulse width = 5 SYSCLK cycles.
0101: /WR and /RD pulse width = 6 SYSCLK cycles.
0110: /WR and /RD pulse width = 7 SYSCLK cycles.
0111: /WR and /RD pulse width = 8 SYSCLK cycles.
1000: /WR and /RD pulse width = 9 SYSCLK cycles.
1001: /WR and /RD pulse width = 10 SYSCLK cycles.
1010: /WR and /RD pulse width = 11 SYSCLK cycles.
1011: /WR and /RD pulse width = 12 SYSCLK cycles.
1100: /WR and /RD pulse width = 13 SYSCLK cycles.
1101: /WR and /RD pulse width = 14 SYSCLK cycles.
1110: /WR and /RD pulse width = 15 SYSCLK cycles.
1111: /WR and /RD pulse width = 16 SYSCLK cycles.
Bits1-0:
EAH1-0: EMIF Address Hold Time Bits.
00: Address hold time = 0 SYSCLK cycles.
01: Address hold time = 1 SYSCLK cycle.
10: Address hold time = 2 SYSCLK cycles.
11: Address hold time = 3 SYSCLK cycles.
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Reset Value
EAS1
EAS0
ERW3
EWR2
EWR1
EWR0
EAH1
EAH0
11111111
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
SFR Address:
SFR Page:
0xA1
0
Summary of Contents for C8051F120
Page 2: ...C8051F120 1 2 3 4 5 6 7 2 Rev 1 2 Notes ...
Page 8: ...C8051F120 1 2 3 4 5 6 7 8 Rev 1 2 26 2 Flash Programming Commands 318 26 3 Debug Support 321 ...
Page 16: ...C8051F120 1 2 3 4 5 6 7 16 Rev 1 2 Notes ...
Page 48: ...C8051F120 1 2 3 4 5 6 7 48 Rev 1 2 ...
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