![Texas Instruments AM1808 Technical Reference Manual Download Page 1240](http://html.mh-extra.com/html/texas-instruments/am1808/am1808_technical-reference-manual_10945581240.webp)
Architecture
1240
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
25.2.13.2 Interrupt Multiplexing
The RINT and XINT interrupts generated by the McBSP peripheral to the CPU are multiplexed with other
interrupt sources. Refer to the device-specific data manual to determine how pin multiplexing affects the
McBSP.
25.2.14 EDMA Event Support
25.2.14.1 Receive Ready Status: REVT and RRDY
RRDY = 1 in the serial port control register (SPCR) indicates that the RBR contents have been copied to
DRR and that the data can now be read by the EDMA controller. Once that data has been read by the
EDMA controller, RRDY is cleared to 0. Also, at device reset or serial port receiver reset (RRST = 0 in
SPCR), the RRDY bit is cleared to 0 to indicate that no data has been received and loaded into DRR.
RRDY directly drives the McBSP receive event to the EDMA controller (via REVT).
For detailed information on using the EDMA to read or write to the McBSP, see the
Enhanced Direct
Memory Access (EDMA3) Controller
chapter.
25.2.14.2 Transmit Ready Status: XEVT and XRDY
XRDY = 1 in the serial port control register (SPCR) indicates that the DXR contents have been copied to
XSR and that DXR is ready to be loaded with a new data word. When the transmitter transitions from
reset to non-reset (XRST transitions from 0 to 1 in SPCR), XRDY also transitions from 0 to 1 indicating
that DXR is ready for new data. Once new data is loaded by the EDMA controller, the XRDY bit is cleared
to 0. However, once this data is copied from DXR to XSR, the XRDY bit transitions again from 0 to 1. The
EDMA controller can write to DXR although XSR has not yet been shifted out on DX. XRDY directly drives
the transmit synchronization event to the EDMA controller (via XEVT).
For detailed information on using the EDMA to read or write to the McBSP, see the
Enhanced Direct
Memory Access (EDMA3) Controller
chapter.
NOTE:
If the polling method is used to service the transmitter, the CPU should wait for one McBSP
bit clock (CLKX) before polling again to write the next element in DXR. This is because
XRDY transitions occur based on bit clock and not CPU clock. The CPU clock is much faster
and can cause false XRDY status, leading to data errors due to overwrites.