SPI Shift Clock
(Module Generated
Internal Clock)
SPICLKO
(POL=1)
SPIENO
SPICLKO
(POL=0)
TCS = 0.5
TCS = 1.5
TCS = 2.5
TCS = 3.5
TCS = 0.5
TCS = 1.5
TCS = 2.5
TCS = 3.5
Functional Description
24.3.2.8 Chip-Select Timing Control
The chip select timing control is only available in master mode with automatic chip select generation
(FORCE bit field is cleared to 0), to add a programmable delay between chip select assertion and first
clock edge or chip select removal and last clock edge. The option is available only in 4 pin mode
MCSPI_MODULCTRL[1] PIN34 is cleared to 0.
This mode is programmable per channel (bit TCS of the register MCSPI_CH(I)CONF).
shows the chip-select SPIEN timing control.
Figure 24-12. Chip-Select SPIEN Timing Controls
NOTE:
Because of the design implementation for transfers using a clock divider ratio set to 1 (clock
bypassed), a half cycle must be added to the value between chip-select assertion and the
first clock edge with PHA = 1 or between chip-select removal and the last clock edge with
PHA = 0.
With an odd clock divider ratio which occurs when granularity is one clock cycle, that means that
MCSPI_CH(I)CONF[CLKG] is set to 1 and MCSPI_CH(I)CONF[CLKD] has an even value, the clock duty
cycle is not 50%, then one of the high level or low level duration is selected to be added to TCS delay.
summarizes all delays between chip select and first (setup) or last (hold) clock edge.
In 3-pin mode this option is useless, the chip select SPIEN is forced to low state.
Table 24-6. Chip Select
↔
Clock Edge Delay Depending on Configuration
Clock Ratio F
ratio
Clock
Chip Select
↔
Clock Edge Delay
Phase
Setup
Hold
PHA
1
0
T_ref × (TCS + ½)
T_ref × (TCS + 1)
1
T_ref × (TCS + 1)
T_ref × (TCS + ½)
Even
≥
2
x
T_ref × F
ratio
× (TCS + ½)
T_ref × F
ratio
× (TCS + ½)
Odd
≥
3 (only with
0
T_ref × [{F
ratio
× TCS) + (F
ratio
+ ½)]
T_ref × [{F
ratio
× TCS) + (F
ratio
+ ½)]
MCSPI_CH(I)CONF[CLK
1
T_ref × [{F
ratio
× TCS) + (F
ratio
- ½)]
T_ref × [{F
ratio
× TCS) + (F
ratio
- ½)]
G] set to 1
T_ref = CLKSPIREF period in ns. F
ratio
= SPI clock division ratio
The clock divider ratio depends on divider granularity MCSPI_CH(I)CONF[CLKG]:
•
MCSPI_CH(I)CONF[CLKG] = 0 : granularity is power of two.
F
ratio
= 2
MCSPI_CH(I)CONF[CLKD]
•
MCSPI_CH(I)CONF[CLKG] = 0 : granularity is power of two.
4011
SPRUH73H – October 2011 – Revised April 2013
Multichannel Serial Port Interface (McSPI)
Copyright © 2011–2013, Texas Instruments Incorporated