
Resetting and Initializing a McBSP
Emulation, Power, and Reset Considerations
10-6
SPRU592E
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McBSP reset.
When the receiver and transmitter reset bits, RRST and
XRST, are loaded with 0s, the respective portions of the McBSP are reset,
and activity in the corresponding section of the serial port stops. All
input-only pins, such as DR and CLKS, and all other pins that are
configured as inputs, are in a known state. The FSR and FSX pins are
driven to their inactive state if they are not outputs. If the CLKR and CLKX
pins are programmed as outputs, they will be driven by CLKG, provided
that GRST = 1. Lastly, the DX pin will be in the high-impedance state when
the transmitter and/or the device is reset.
During normal operation, the sample rate generator is reset if the GRST bit
is cleared. GRST should be 0 only when neither the transmitter nor the
receiver is using the sample rate generator. In this case, the internal
sample rate generator clock (CLKG) and its frame-sync signal (FSG) are
driven inactive low.
When the sample rate generator is not in the reset state (GRST = 1), pins
FSR and FSX are in an inactive state when RRST = 0 and XRST = 0,
respectively, even if they are outputs driven by FSG. This ensures that
when only one portion of the McBSP is in reset, the other portion can
continue operation when FRST = 1 and its frame synchronization is driven
by FSG.
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Sample rate generator reset.
The sample rate generator is reset when
the DSP is reset or when GRST is loaded with 0. In the case of a DSP reset,
the sample rate generator clock, CLKG, is driven by the McBSP internal
input clock divided by 2, and the frame-sync signal, FSG, is driven inactive
low.
When neither the transmitter nor the receiver is fed by CLKG and FSG,
you can reset the sample rate generator by clearing GRST. In this case,
CLKG and FSG are driven inactive low. If you then set GRST, CLKG starts
and runs as programmed. Later, if FRST = 1, FSG pulses active high after
the programmed number of CLKG cycles has elapsed.
10.4.3 McBSP Initialization Procedure
The serial port initialization procedure is as follows:
1) Make XRST = RRST = FRST = GRST = 0 in SPCR[1,2]. If coming out of
a DSP reset, this step is not required.
2) While the serial port is in the reset state, program only the McBSP
configuration registers (not the data registers) as required.
3) Wait for two clock cycles. This ensures proper internal synchronization.
Содержание TMS320VC5509
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