Receiver Configuration
1079
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
C28 Multichannel Buffered Serial Port (McBSP)
15.8.2 Resetting and Enabling the Receiver
The first step of the receiver configuration procedure is to reset the receiver, and the last step is to enable
the receiver (to take it out of reset).
describes the bits used for both of these steps.
Table 15-18. Register Bits Used to Reset or Enable the McBSP Receiver Field Descriptions
Register
Bit
Field
Value
Description
SPCR2
7
FRST
Frame-synchronization logic reset
0
Frame-synchronization logic is reset. The sample rate generator does not generate frame-
synchronization signal FSG, even if GRST = 1.
1
If GRST = 1, frame-synchronization signal FSG is generated after (FPER + 1) number of
CLKG clock cycles; all frame counters are loaded with their programmed values.
SPCR2
6
GRST
Sample rate generator reset
0
Sample rate generator is reset. If GRST = 0 due to a DSP reset, CLKG is driven by the
CPU clock divided by 2, and FSG is driven low (inactive). If GRST = 0 due to program
code, CLKG and FSG are both driven low (inactive).
1
Sample rate generator is enabled. CLKG is driven according to the configuration
programmed in the sample rate generator registers (SRGR[1,2]). If FRST = 1, the
generator also generates the frame-synchronization signal FSG as programmed in the
sample rate generator registers.
SPCR1
0
RRST
Receiver reset
0
The serial port receiver is disabled and in the reset state.
1
The serial port receiver is enabled.
15.8.2.1 Reset Considerations
The serial port can be reset in the following two ways:
1. The DSP reset (XRS signal driven low) places the receiver, transmitter, and sample rate generator in
reset. When the device reset is removed (XRS signal released), GRST = FRST = RRST = XRST = 0
keep the entire serial port in the reset state, provided the McBSP clock is turned on.
2. The serial port transmitter and receiver can be reset directly using the RRST and XRST bits in the
serial port control registers. The sample rate generator can be reset directly using the GRST bit in
SPCR2.
shows the state of McBSP pins when the serial port is reset due to a device reset and a
direct receiver/transmitter reset.
For more details about McBSP reset conditions and effects, see
,
Resetting and Initializing
a McBSP
.
Table 15-19. Reset State of Each McBSP Pin
Pin
Possible
State(s)
State Forced By Device
Reset
State Forced By Receiver Reset
(RRST = 0 and GRST = 1)
MDRx
I
GPIO Input
Input
MCLKRx
I/O/Z
GPIO Input
Known state if input; MCLKR running if output
MFSRx
I/O/Z
GPIO Input
Known state if input; FSRP inactive state if output
Transmitter reset (XRST = 0 and GRST = 1)
MDXx
O/Z
GPIO Input
Low impedance after transmit bit clock provided
MCLKXx
I/O/Z
GPIO Input
Known state if input; CLKX running if output
MFSXx
I/O/Z
GPIO Input
Known state if input; FSXP inactive state if output
15.8.3 Set the Receiver Pins to Operate as McBSP Pins
To configure a pin for its McBSP function , you should configure the bits of the GPxMUXn register
appropriately. In addition to this, bits 12 and 13 of the PCR register must be set to 0. These bits are
defined as reserved.
