2
N S 9 7 5 0 B - A 1 E r r a t a , R e v . F 0 9 / 2 0 0 6
S P I s l a v e d a t a o u t p u t h i g h i m p e d a n c e c o n t r o l
SPI slave data output high impedance control
There is a problem that occurs in slave mode when there are other slaves on the SPI bus. When the
slave select signal is de-asserted, the data output pin fails to go into a high impedance state and
interferes with any other slave that is trying to drive the data signal.
Workaround: Do this for each SPI port. Externally buffer the data_out signal with a tri-state buffer
and connect the select signal to the active low tri-state control pin. There should be a pullup
resistor on the output of the buffer to prevent floating when no slaves are selected.
Example:
UART gap timer
The start bit of a new character may not be detected when the character or buffer gap timer
expires. Framing, parity, or data corruption occur when a start bit is missed.
Software workaround: Three conditions have been identified for this erratum:
Applications with a steady stream of receive data are not affected if the buffer gap timer is
disabled.
Applications where the gap between characters is fixed and the character gap timer period is
configured to be less than the fixed period. The buffer gap timer must be disabled.
Applications that have higher-level protocol error detection and recovery such as PPP can use
both the buffer and character gap timers.
Hardware workaround:
Note:
The hardware workaround requires that you have installed the appropriate software patch
found in the NETOS SW Toolkit (on the Web).
A hardware workaround eliminates the possibility of receiving a start bit when a character or buffer
gap timer is expiring. The workaround drives the baud clock off-chip and synchronizes the incoming
data with this clock. As a result, the buffer and character gap timers and the next start bit have a
fixed and known relationship with each other.
slave_select_n
( from ASIC ) dout
dout ( to bus )
Summary of Contents for Errata NS9750B-A1
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