Signal/Connection Descriptions
Table 7. Serial Host Interface Signals (Continued)
State
Signal
Name
Signal
Type
during
Reset
Signal Description
Input
Input
Tri-stated SPI Slave Select—This signal is an active low Schmitt-trigger input when
configured for the SPI mode. When configured for the SPI Slave mode, this
signal is used to enable the SPI slave for transfer. When configured for the SPI
master mode, this signal should be kept deasserted (pulled high). If it is
asserted while configured as SPI master, a bus error condition is flagged. If SS
is deasserted, the SHI ignores SCK clocks and keeps the MISO output signal in
the high-impedance state.
SS
HA2
I2C Slave Address 2—This signal uses a Schmitt-trigger input when
configured for the I2C mode. When configured for the I2C Slave mode, the HA2
signal is used to form the slave device address. HA2 is ignored in the I2C
master mode.
This signal is tri-stated during hardware, software and individual reset. Thus,
there is no need for an external pull-up in this state.
Internal Pull up resistor.
This input is 5 V tolerant.
Input or
Output
Tri-stated Host Request—This signal is an active low Schmitt-trigger input when
configured for the master mode but an active low output when configured for the
slave mode.
HREQ
When configured for the slave mode, HREQ is asserted to indicate that the SHI
is ready for the next data word transfer and deasserted at the first clock pulse of
the new data word transfer. When configured for the master mode, HREQ is an
input. When asserted by the external slave device, it will trigger the start of the
data word transfer by the master. After finishing the data word transfer, the
master will await the next assertion of HREQ to proceed to the next transfer.
This signal is tri-stated during hardware, software, personal reset, or when the
HREQ1–HREQ0 bits in the HCSR are cleared. There is no need for an external
pull-up in this state.
Internal Pull up resistor.
This input is 5 V tolerant.
16
DSP56371 Technical Data
Freescale Semiconductor
FREESCALE [ Freescale ]
