SPRS292 − OCTOBER 2005
MULTICHANNEL BUFFERED SERIAL PORT TIMING (CONTINUED)
switching characteristics over recommended operating conditions for McBSP as SPI master or slave: CLKSTP = 10b, CLKXP = 0†‡ (see Figure 48)
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| GDPA−167 |
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| ZDPA−167 |
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| PARAMETER |
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| −200 |
| UNIT |
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| −250 |
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| MASTER§ | SLAVE |
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| MIN | MAX | MIN | MAX |
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1 | Hold time, FSX low | T − 2 | T + 3 |
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after CLKX low¶ |
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2 | Delay time, FSX low to CLKX high# | L − 2 | L + 3 |
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3 | Delay time, CLKX high to DX valid | −3 | 4 | 6P + 2 | 10P + 17 | ns | |
6 | Disable time, DX high impedance following last data bit from | L − 2 | L + 3 |
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CLKX low |
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7 | Disable time, DX high impedance following last data bit from |
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| 2P + 3 | 6P + 17 | ns | |
FSX high |
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8 | Delay time, FSX low to DX valid |
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| 4P + 2 | 8P + 17 | ns |
†P = 1/CPU clock frequency in ns. For example, when running parts at 250 MHz, use P = 4 ns.
‡For all SPI slave modes, CLKG is programmed as 1/2 of the CPU clock by setting CLKSM = CLKGDV = 1. § S = Sample rate generator input clock = 2P if CLKSM = 1 (P = 1/CPU clock frequency)
=Sample rate generator input clock = P_clks if CLKSM = 0 (P_clks = CLKS period)
T = | CLKX period = (1 + CLKGDV) * S | |
H = | CLKX high pulse width | = (CLKGDV/2 + 1) * S if CLKGDV is even |
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| = (CLKGDV + 1)/2 * S if CLKGDV is odd or zero |
L = | CLKX low pulse width | = (CLKGDV/2) * S if CLKGDV is even |
=(CLKGDV + 1)/2 * S if CLKGDV is odd or zero
¶FSRP = FSXP = 1. As a SPI master, FSX is inverted to provide
CLKXM = FSXM = 1, CLKRM = FSRM = 0 for master McBSP CLKXM = CLKRM = FSXM = FSRM = 0 for slave McBSP
#FSX should be low before the rising edge of clock to enable slave devices and then begin a SPI transfer at the rising edge of the master clock (CLKX).
CLKX |
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| 1 | 2 |
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FSX |
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| 7 | 8 |
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| 6 |
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DX | Bit 0 |
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| 4 | 5 |
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DR | Bit 0 |
Figure 48. McBSP Timing as SPI Master or Slave: CLKSTP = 10b, CLKXP = 0
POST OFFICE BOX 1443 • HOUSTON, TEXAS 77251−1443 | 95 |