Freescale Semiconductor DSP56366 7.4.1 SHI Input/Output Shift Register (IOSR)Host Side

Serial Host Interface Programming Model
DSP56366 24-Bit Digital Signal Processor User Manual, Rev. 4
Freescale Semiconductor 7-5
The SHI interrupt vector table is shown in Tabl e 7-1 and the exception priorities generated by the SHI are
shown in Tabl e 7-2.
7.4.1 SHI Input/Output Shift Register (IOSR)—Host Side
The variable length Input/Output Shift Register (IOSR) can be viewed as a serial-to-parallel and
parallel-to-serial buffer in the SHI. The IOSR is involved with every data transfer in both directions (read
and write). In compliance with the I2C and SPI bus protocols, data is shifted in and out MSB first. In 8-bit
data transfer modes, the most significant byte of the IOSR is used as the shift register. In 16-bit data
transfer modes, the two most significant bytes become the shift register. In 24-bit transfer modes, the shift
register uses all three bytes of the IOSR (see Figure 7-5).
NOTE
The IOSR cannot be accessed directly either by the host processor or by the
DSP. It is fully controlled by the SHI controller logic.
Table7- 1 SHI Interrupt Vectors
Program Address Interrupt Source
VBA:$0040 SHI Transmit Data
VBA:$0042 SHI Transmit Underrun Error
VBA:$0044 SHI Receive FIFO Not Empty
VBA:$0048 SHI Receive FIFO Full
VBA:$004A SHI Receive Overrun Error
VBA:$004C SHI Bus Error
Table7-2 SHI Internal Interrupt Priorities
Priority Interrupt
Highest SHI Bus Error
SHI Receive Overrun Error
SHI Transmit Underrun Error
SHI Receive FIFO Full
SHI Transmit Data
Lowest SHI Receive FIFO Not Empty