SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
There are three scenarios to provide clock source signals for the Tx part and four scenarios for the Rx part of the McASP serializers. The first three scenarios are identical between the Tx and Rx part of the McASP. They feature an asynchronous operation between receiver and transmitter channels using independent Tx/Rx bit rate clock sources (either internal or external).
In the first scenario, the transmit - XCLK and receive - RCLK serial clocks (clock at the bit rate) are generated internally by passing through a couple of clock dividers off the internal functional clock source (AUXCLK). In this case, the bit rate clock is generated internally and is driven out on the pin ACLKX for the Tx part and pin ACLKR for the Rx part, respectively. An internally generated high-frequency clock can be optionally driven out onto the AHCLKX pin for the Tx part to serve as a reference clock for other components in the system.
In the second scenario, an external for the device clock, is passed on the ACLKX (for the TX part) and ACLKR (for the RX part) pins which are configured as inputs. In this case the Rx- /Tx- high-speed clock logic is bypassed for the XCLK/RCLK generation.
In the third (mixed) scenario, an externally driven (master) high-frequency clock is applied on the AHCLKX (for the TX part) pin, which is configured as input. In this case the AHCLKX clock frequency can be divided down via programming the ACLKX associated divider to produce the necessary bit rate clock. The high-speed clock divider can NOT be used.
In the fourth clock generation scenario the bit rate clock for McASP receivers - RCLK is derived from the bit rate clock of the McASP transmitters - XCLK for a synchronous operation between transmitters and receivers. Hence, the whole receiver clock generator logic is bypassed.
A typical role of the McASP frame sync signal is to carry the left/right clock (LRCLK) signal when transmitting and receiving stereo data.
For an asynchronous operation, the AFSX (Tx part) and AFSR (Rx part) frame synchronization signals can be sourced internally or delivered externally independently for the Tx and Rx channels. During synchronous operation the receive frame sync - AFSR signal is derived from the transmit frame sync - AFSX signal. A synchronous and asynchronous mode applies to bit rate clock and frame sync signals at the same time.