Serial Communication Interface (SCI)
SCI Programming Model
MOTOROLA
DSP56309UM/D 8-19
8.3.4.1
SCI Receive Registers (SRX)
Data bits received on the RXD signal are shifted into the SCI receive shift register. When
a complete word has been received, the data portion of the word is transferred to the
byte-wide SRX. This process converts the serial data to parallel data and provides
double-buffering. Double-buffering provides flexibility to the programmer and
increased throughput since the programmer can save (and process) the previous word
while the current word is being received.
The SRX can be read at three locations as SRXL, SRXM, and SRXH. When SRXL is read,
the contents of the SRX are placed in the lower byte of the data bus and the remaining
bits on the data bus are read as 0s. Similarly, when SRXM is read, the contents of SRX are
placed in the middle byte of the bus, and when SRXH is read, the contents of SRX are
placed in the high byte with the remaining bits read as 0s. Mapping SRX as described
allows three bytes to be efficiently packed into one 24-bit word by ORing three data
bytes read from the three addresses.
Figure 8-7
SCI Programming Model Data Registers
SRX
SRX
SRX
RXD
SCI Receive Data Shift Register
Note: 1. SRX is the same register decoded at three different addresses.
STX
STX
STX
TXD
SCI Transmit Data Shift Register
Note: 1. Bytes are masked on the fly.
2. STX is the same register decoded at four different addresses.
STXA
(a) Receive Data Register
(b) Transmit Data Register
AA0694
SCI Receive Data Register High (Read Only)
SCI Receive Data Register Middle (Read Only)
SCI Receive Data Register Low (Read Only)
0
7
8
15
16
23
0
7
8
15
16
23
0
7
8
15
16
23
SCI Transmit Data Register High (Write Only)
SCI Transmit Data Register Middle (Write Only)
SCI Transmit Data Register Low (Write Only)
SCI Transmit Data Address Register (Write Only)
Содержание DSP56309
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Страница 125: ...5 2 DSP56309UM D MOTOROLA General Purpose I O 5 1 INTRODUCTION 5 3 5 2 PROGRAMMING MODEL 5 3 ...
Страница 128: ...MOTOROLA DSP56309UM D 6 1 SECTION 6 HOST INTERFACE HI08 ...
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Страница 242: ...MOTOROLA DSP56309UM D 9 1 SECTION 9 TRIPLE TIMER MODULE ...
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Страница 302: ...MOTOROLA DSP56309UM D 11 1 SECTION 11 JTAG PORT ...
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Страница 370: ...MOTOROLA DSP56309UM D D 1 APPENDIX D PROGRAMMING REFERENCE ...
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