TMS320VC5421 datasheet(87/104 Pages) TI1

87 / 104 page

Electrical Specifications

December 1999 − Revised October 2008

SPRS098D

5.14.4

McBSP as SPI Master or Slave Timing

The following timing requirements and switching characteristics tables assume testing over recommended

operating conditions and H = 0.5tc(CO) (see Figure 5−23, Figure 5−24, Figure 5−25, and Figure 5−26).

Table 5−27. McBSP as SPI Master or Slave Timing Requirements (CLKSTP = 10b, CLKXP = 0)†

MASTER

SLAVE

UNIT

MIN

MAX

MIN

MAX

UNIT

tsu(BDRV-BCKXL)

Setup time, BDR valid before BCLKX low

2 − 12H

th(BCKXL-BDRV)

Hold time, BDR valid after BCLKX low

6 + 12H

tsu(BFXL-BCKXH)

Setup time, BFSX low before BCLKX high

tc(BCKX)

Cycle time, BCLKX

12H

32H

† For all SPI slave modes, CLKG is programmed as 1/2 of the CPU clock by setting CLKSM = CLKGDV = 1.

Table 5−28. McBSP as SPI Master or Slave Switching Characteristics (CLKSTP = 10b, CLKXP = 0)†

PARAMETER

MASTER‡

SLAVE

UNIT

PARAMETER

MIN

MAX

MIN

MAX

UNIT

th(BCKXL-BFXL)

Hold time, BFSX low after BCLKX low§

T − 5

T + 6

td(BFXL-BCKXH)

Delay time, BFSX low to BCLKX high¶

C − 5

C + 5

td(BCKXH-BDXV)

Delay time, BCLKX high to BDX valid

−3

6H + 4

10H + 19

tdis(BCKXL-BDXHZ)

Disable time, BDX high impedance following last data bit from BCLKX

low

C − 6

C +10

tdis(BFXH-BDXHZ)

Disable time, BDX high impedance following last data bit from BFSX

high

4H+ 4

8H + 17

td(BFXL-BDXV)

Delay time, BFSX low to BDX valid

4H + 4

8H + 17

† 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-BCKXL)

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 5−23. McBSP Timing as SPI Master or Slave: CLKSTP = 10b, CLKXP = 0

TMS320VC5421 Datasheet(PDF) 87 Page - Texas Instruments

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