15.5.7.1 Disabling or Enabling Versus Masking or Unmasking
For transmission, a channel can be:
• Enabled and unmasked (transmission can begin and can be completed)
• Enabled but masked (transmission can begin but cannot be completed)
• Disabled (transmission cannot occur)
The following definitions explain the channel control options:
Enabled channel
A channel that can begin transmission by passing data from the data
transmit register(s) (DXR(s)) to the transmit shift registers (XSR(s)).
Masked channel
A channel that cannot complete transmission. The DX pin is held in the high
impedance state; data cannot be shifted out on the DX pin.
In systems where symmetric transmit and receive provides software
benefits, this feature allows transmit channels to be disabled on a shared
serial bus. A similar feature is not needed for reception because multiple
receptions cannot cause serial bus contention.
Disabled channel
A channel that is not enabled. A disabled channel is also masked.
Because no DXR-to-XSR copy occurs, the XRDY bit of SPCR2 is not set.
Therefore, no DMA synchronization event (XEVT) is generated, and if the
transmit interrupt mode depends on XRDY (XINTM = 00b in SPCR2), no
interrupt is generated.
The XEMPTY bit of SPCR2 is not affected.
Unmasked channel
A channel that is not masked. Data in the XSR(s) is shifted out on the DX
pin.
15.5.7.2 Activity on McBSP Pins for Different Values of XMCM
shows the activity on the McBSP pins for the various XMCM values. In all cases, the transmit frame
is configured as follows:
• XPHASE = 0: Single-phase frame (required for multichannel selection modes)
• XFRLEN1 = 0000011b: 4 words per frame
• XWDLEN1 = 000b: 8 bits per word
• XMCME = 0: 2-partition mode (only partitions A and B used)
In the case where XMCM = 11b, transmission and reception are symmetric, which means the corresponding
bits for the receiver (RPHASE, RFRLEN1, RWDLEN1, and RMCME) must have the same values as XPHASE,
XFRLEN1, and XWDLEN1, respectively.
In the figure, the arrows showing where the various events occur are only sample indications. Wherever
possible, there is a time window in which these events can occur.
15.5.7.3 Using Interrupts Between Block Transfers
When a multichannel selection mode is used, an interrupt request can be sent to the CPU at the end of every
16-channel block (at the boundary between partitions and at the end of the frame). In the receive multichannel
selection mode, a receive interrupt (RINT) request is generated at the end of each block transfer if RINTM =
01b. In any of the transmit multichannel selection modes, a transmit interrupt (XINT) request is generated at
the end of each block transfer if XINTM = 01b. When RINTM/XINTM = 01b, no interrupt is generated unless a
multichannel selection mode is on.
These interrupt pulses are active high and last for two CPU clock cycles.
This type of interrupt is especially helpful if you are using the two-partition mode (described in
and you want to know when you can assign a different block of channels to partition A or B.
Multichannel Buffered Serial Port (McBSP)
910
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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