SPRS079E – OCTOBER 1998 – REVISED AUGUST 2000
57
POST OFFICE BOX 1443
•
HOUSTON, TEXAS 77251–1443
multichannel buffered serial port timing (continued)
timing requirements for McBSP as SPI master or slave: [H=0.5t
c(CO)
] CLKSTP = 10b, CLKXP = 0
†
(see Figure 31)
MASTER
SLAVE
UNIT
MIN
MAX
MIN
MAX
UNIT
tsu(BDRV-BCKXL)
Setup time, BDR valid before BCLKX low
9
– 12H
ns
th(BCKXL-BDRV)
Hold time, BDR valid after BCLKX low
0
5 + 12H
ns
tsu(BFXL-BCKXH)
Setup time, BFSX low before BCLKX high
10
ns
tc(BCKX)
Cycle time, BCLKX
12H
32H
ns
† For all SPI slave modes, CLKG is programmed as 1/2 of the CPU clock by setting CLKSM = CLKGDV = 1.
switching characteristics for McBSP as SPI master or slave: [H=0.5t
c(CO)
] CLKSTP = 10b,
CLKXP =
0† (see Figure 31)
PARAMETER
MASTER
‡
SLAVE
UNIT
PARAMETER
MIN
MAX
MIN
MAX
UNIT
th(BCKXL-BFXL)
Hold time, BFSX low after BCLKX low§
T – 3
T + 4
ns
td(BFXL-BCKXH)
Delay time, BFSX low to BCLKX high¶
C – 5
C + 3
ns
td(BCKXH-BDXV)
Delay time, BCLKX high to BDX valid
–2
6
6H + 5
10H + 15
ns
tdis(BCKXL-BDXHZ)
Disable time, BDX high impedance following last data bit from
BCLKX low
C – 2
C + 3
ns
tdis(BFXH-BDXHZ)
Disable time, BDX high impedance following last data bit from
BFSX high
2H+ 4
6H + 17
ns
td(BFXL-BDXV)
Delay time, BFSX low to BDX valid
4H – 2
8H + 17
ns
† For all SPI slave modes, CLKG is programmed as 1/2 of the CPU clock by setting CLKSM = CLKGDV = 1.
‡ T = BCLKX period = (1 + CLKGDV) * 2H
C =
BCLKX low pulse width = T/2 when CLKGDV is odd or zero and = (CLKGDV/2) * 2H when CLKGDV is even
§ FSRP = FSXP = 1. As a SPI master, BFSX is inverted to provide active-low slave-enable output. As a slave, the active-low signal input on BFSX
and BFSR is inverted before being used internally.
CLKXM = FSXM = 1, CLKRM = FSRM = 0 for master McBSP
CLKXM = CLKRM = FSXM = FSRM = 0 for slave McBSP
¶ BFSX 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
(BCLKX).
Bit 0
Bit(n-1)
(n-2)
(n-3)
(n-4)
Bit 0
Bit(n-1)
(n-2)
(n-3)
(n-4)
BCLKX
BFSX
BDX
BDR
tsu(BDRV-BCLXL)
td(BCKXH-BDXV)
th(BCKXL-BDRV)
tdis(BFXH-BDXHZ)
tdis(BCKXL-BDXHZ)
th(BCKXL-BFXL)
td(BFXL-BDXV)
td(BFXL-BCKXH)
LSB
MSB
tsu(BFXL-BCKXH)
tc(BCKX)
Figure 31. McBSP Timing as SPI Master or Slave: CLKSTP = 10b, CLKXP = 0