Motorola DSP56012 - Manual (Page 162)

5-14 DSP56012 User’s Manual MOTOROLA
Serial Host Interface
Serial Host Interface Programming Model
reset be generated (HEN cleared) before changing HI
2
C. HI
2
C is cleared during
hardware reset and software reset.
5.4.6.3 HCSR Serial Host Interface Mode (HM[1:0])—Bits 3–2
The read/write control bits HM[1:0] select the size of the data words to be
transferred, as shown in
Table 5-4 on page 5-14. HM[1:0] should be modified only
when the SHI is idle (HBUSY = 0). HM[1:0] are cleared during hardware reset and
software reset.
5.4.6.4 HCSR Reserved Bits—Bits 23, 18, 16, and 4
These bits in HCSR are reserved and unused. They are read as 0s and should be
written with 0s for future compatibility.
5.4.6.5 HCSR FIFO-Enable Control (HFIFO)—Bit 5
The read/write control bit HCSR FIFO-enable control (HFIFO) selects the size of the
receive FIFO. When HFIFO is cleared, the FIFO has a single level. When HFIFO is set,
the FIFO has 10 levels. It is recommended that an SHI individual reset be generated
(HEN cleared) before changing HFIFO. HFIFO is cleared during hardware reset and
software reset.
5.4.6.6 HCSR Master Mode (HMST)—Bit 6
The read/write control bit HCSR Master (HMST) determines the operating mode of
the SHI. If HMST is set, the interface operates in the Master mode. If HMST is
cleared, the interface operates in the Slave mode. The SHI supports a single-master
configuration, in both I
2
C and SPI modes. When configured as an SPI Master, the SHI
drives the SCK line and controls the direction of the data lines MOSI and MISO. The
SS line must be held deasserted in the SPI Master mode; if the SS line is asserted
when the SHI is in SPI Master mode, a bus error will be generated (the HCSR HBER
bit will be set—see
Section 5.4.6.17 Host Bus Error (HBER)—Bit 21 ). When
configured as an I
2
C Master, the SHI controls the I
2
C bus by generating start events,
clock pulses, and stop events for transmission and reception of serial data. It is
Table 5-4 SHI Data Size
HM1 HMO Description
0 0 8-bit data
0 1 16-bit data
1 0 24-bit data
1 1 Reserved