Data Transmission and Reception
11-29
Multichannel Buffered Serial Ports
Figure 11–10.
Single-Phase Frame of Four 8-Bit Elements
DX
FSX
CLKX
DR
FSR
CLKR
Element 4
Element 3
Element 2
Element 1
DXR-to-XSR copy
DXR-to-XSR copy
DXR-to-XSR copy
DXR-to-XSR copy
ÁÁ
ÁÁ
Á
Á
Á
Á
ÁÁ
ÁÁ
ÁÁ
Á
RBR–to-DRR copy
RBR-to-DRR copy
RBR-to-DRR copy
RBR–to–DRR copy
The example in Figure 11–10 can also be viewed as a data stream of a single-
phase frame of one 32-bit data element, as shown in Figure 11–11. In this
case:
-
(R/X)PHASE = 0, indicating a single phase frame
-
(R/X)FRLEN1 = 0b, indicating a 1-element frame
-
(R/X)WDLEN1 = 101b, indicating 32-bit elements
In this situation, one 32-bit data element is transferred to and from the McBSP
by the CPU or the DMA controller. Thus, one read of DRR and one write of DXR
is necessary for each frame. As a result, the number of transfers is one fourth
that of the previous case. This manipulation reduces the percentage of bus
time required for serial port data movement.
Figure 11–11.Single-Phase Frame of One 32-Bit Element
Element 1
DXR to XSR Copy
RBR to DRR copy
CLKR
FSR
DR
CLKX
FSX
DX