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Architecture
1241
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
25.2.15 Power Management
The McBSP can be placed in reduced power modes to conserve power during periods of low activity. The
power management of the peripheral is controlled by the processor Power and Sleep Controller (PSC).
The PSC acts as a master controller for power management for all of the peripherals on the device.
In order for the McBSP to be placed in power-down mode by the PSC, ensure that the XRDY and RRDY
flags in the serial port control register (SPCR) are cleared by performing the following steps:
1. Place the McBSP in reset by clearing the XRST, RRST, FRST, and GRST bits to 0 in SPCR.
If EDMA is being used to service the transmitter and/or the receiver, disable the associated EDMA
channels.
For detailed information on using the EDMA to read or write to the McBSP, see the
Enhanced Direct
Memory Access (EDMA3) Controller
chapter.
2. Switch the McBSP clocks and frames to internal clock source:
(a) Set the CLKSM and FSGM bits to 1 in the sample rate generator register (SRGR).
(b) Set the CLKXM, CLKRM, FSXM, and FSRM bits to 1 in the pin control register (PCR).
(c) Clear the SCLKME bit to 0 in PCR.
3. Bring the McBSP out of reset by setting the XRST, RRST, and GRST bits to 1 in SPCR.
4. Wait for two CLKSRG cycles for proper internal synchronization.
5. Write a dummy data value to the data transmit register (DXR) in order to clear the first XRDY flag.
6. Wait for at least one McBSP bit clock, since once the first dummy data value is internally copied from
DXR to XSR, the XRDY flag transitions again from 0 to 1.
7. Write a second dummy data value to DXR in order to clear the second XRDY flag.
8. Check the RRDY flag in SPCR and if set to 1, read the data receive register (DRR) and discard the
data to clear the RRDY flag.
9. Place the McBSP in power-down mode by issuing the proper PSC commands. For detailed information
on power management procedures using the PSC, see the
Power and Sleep Controller (PSC)
chapter.
NOTE:
After waking up the McBSP from a power-down mode using the proper PSC commands,
remember to reconfigure the SPCR, SRGR, and PCR registers to the clock and frame
combination that they were in before entering the power-down sequence and discard the two
dummy data values that were used to clear the XRDY flags. If EDMA is used, re-enable the
corresponding EDMA channels.
25.2.16 Emulation Considerations
The FREE and SOFT bits are special emulation bits in the serial port control register (SPCR) that
determine the state of the McBSP when an emulation suspend event occurs in the emulator. An emulation
suspend event corresponds to any type of emulator access to the CPU, such as a hardware or software
breakpoint, a probe point, or a printf instruction.
shows the effects of the FREE and SOFT bits on the response of the McBSP to emulation
suspend events.
Table 25-21. McBSP Emulation Modes Selectable With the FREE and SOFT Bits of SPCR
FREE Bit
in SPCR
SOFT Bit
in SPCR
McBSP Emulation Mode
0
0
Immediate stop mode (reset condition). The transmitter and receiver stop immediately in response
to an emulation suspend event.
0
1
Soft stop mode. When an emulation suspend event occurs, the transmitter stops after completion of
the current word. The receiver is not affected.
1
0 or 1
Free run mode. The transmitter and receiver continue to run when an emulation suspend event
occurs.