Technical Reference Manual
002-29852 Rev. *B
Bits Name
SW
HW
Default or
Enum
Description
0:3
OVS
RW
R
15
Serial interface bit period oversampling factor
expressed in SCB clock cycles. Used for SPI and
UART functionality. OVS + 1 SCB clock cycles
constitute a single serial interface clock/bit cycle. This
field is NOT used in externally clocked mode. If OVS is
odd, the oversampling factor is even and the low and
high phase of the interface clock period are the same.
If OVS is even, the oversampling factor is odd and the
low and high phase can differ by 1 SCB clock period.
In SPI master mode, the valid range is [3, 15]. At an
SCB frequency of 48 MHz, the maximum SPI bit rate is
12 Mbps, assuming ideal (0 ns) IO cell and routing
(chip and board) delay. The calculated maximum bit
rate decreases, when realistic chip and routing delays
are taken into account. The effective system bit rate is
dependent on the external SPI slave that we
communicate with. If the SPI output clock to SPI MISO
input round trip delay is significant (multiple SPI output
clock cycles), it may be necessary to increase OVS
and/or to set SPI_CTRL.LATE_MISO_SAMPLE to '1'
to achieve the maximum possible system bit rate.
In SPI slave mode, the OVS field is NOT used.
However, there is a frequency requirement for the SCB
clock wrt. the SPI input clock (IF) on the interface to
guarantee functional correct behavior. This
requirement is expressed as a ratio: SCB clock/IF
clock. The ratio is dependent on the setting of
RX_CTRL.MEDIAN and the external SPI master's
capability to support 'late MISO sample' functionality
(similar to our SPI master functionality represented by
SPI_CTRL.LATE_MISO_SAMPLE):
- MEDIAN is '0' and external SPI master has NO 'late
MISO sample functionality': SCB clock/IF clock >= 6.
At a SCB frequency of 48 MHz, the maximum bit rate
is 8 Mbps.
- MEDIAN is '0' and external SPI master has 'late
MISO sample functionality': SCB clock/IF clock >= 3.
At a SCB frequency of 48 MHz, the maximum bit rate
is 16 Mbps.
- MEDIAN is '1' and external SPI master has NO 'late
MISO sample functionality': SCB clock/IF clock >= 8.
At a SCB frequency of 48 MHz, the maximum bit rate
is 6 Mbps.
- MEDIAN is '1' and external SPI master has 'late
MISO sample functionality': SCB clock/IF clock >= 4.
At a SCB frequency of 48 MHz, the maximum bit rate
is 12 Mbps.
As discussed earlier, the calculated maximum bit rate
decreases, when realistic chip and routing delays are
taken into account.
In UART standard submode (including LIN), the valid
range is [7, 15]. In UART SmartCard submode, the
valid range is [7, 15].
1382
2022-04-18
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