SPRS293 − OCTOBER 2005
92
POST OFFICE BOX 1443
•
HOUSTON, TEXAS 77251−1443
MULTICHANNEL BUFFERED SERIAL PORT TIMING (CONTINUED)
timing requirements for McBSP as SPI master or slave: CLKSTP = 10b, CLKXP = 1
†‡
(see Figure 45)
−150
NO.
MASTER
SLAVE
UNIT
NO.
MIN
MAX
MIN
MAX
UNIT
4
tsu(DRV-CKXH) Setup time, DR valid before CLKX high
12
2 − 6P
ns
5
th(CKXH-DRV)
Hold time, DR valid after CLKX high
4
5 + 12P
ns
† P = 1/CPU clock frequency in ns. For example, when running parts at 150 MHz, use P = 6.7 ns.
‡ For all SPI slave modes, CLKG is programmed as 1/2 of the CPU clock by setting CLKSM = CLKGDV = 1.
switching characteristics over recommended operating conditions for McBSP as SPI master or
slave: CLKSTP = 10b, CLKXP = 1
†‡
(see Figure 45)
−150
NO.
PARAMETER
MASTER§
SLAVE
UNIT
NO.
PARAMETER
MIN
MAX
MIN
MAX
UNIT
1
th(CKXH-FXL)
Hold time, FSX low after CLKX high¶
T − 2
T + 3
ns
2
td(FXL-CKXL)
Delay time, FSX low to CLKX low#
H − 2
H + 3
ns
3
td(CKXL-DXV)
Delay time, CLKX low to DX valid
−3
4
6P + 2
10P + 17
ns
6
tdis(CKXH-DXHZ)
Disable time, DX high impedance following last data bit from
CLKX high
H − 2
H + 3
ns
7
tdis(FXH-DXHZ)
Disable time, DX high impedance following last data bit from FSX
high
2P + 3
6P + 17
ns
8
td(FXL-DXV)
Delay time, FSX low to DX valid
4P + 2
8P + 17
ns
† P = 1/CPU clock frequency in ns. For example, when running parts at 150 MHz, use P = 6.7 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
= ( 1)/2 * S if CLKGDV is odd or zero
L =
CLKX low pulse width
= (CLKGDV/2) * S if CLKGDV is even
= ( 1)/2 * S if CLKGDV is odd or zero
¶ FSRP = FSXP = 1. As a SPI master, FSX is inverted to provide active-low slave-enable output. As a slave, the active-low signal input on FSX
and FSR is inverted before being used internally.
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).
