received, it is possible that the application code will read the data buffer such that
sufficient room will be made to store the dataword that is being NACKed. Even if room
has been made in the data buffer after the transmission of a NACK is completed, the
received data will always be discarded as a result of an overflow and the
ET7816[RXTHRESHOLD] value will be incremented by one. However, if sufficient
space now exists to write the received data which was NACK'ed, S1[OR] will be blocked
and kept from asserting.
38.9.5 Match address registers
The two match address registers allow a second match address function for a broadcast or
general call address to the serial bus, as an example.
38.9.6 Clearing 7816 wait timer (WT, BWT, CWT) interrupts
The 7816 wait timer interrupts associated with IS7816[WT], IS7816[BWT], and
IS7816[CWT] will automatically reassert if they are cleared and the wait time is still
violated. This behavior is similar to most of the other interrupts on the UART. In most
cases, if the condition that caused the interrupt to trigger still exists when the interrupt is
cleared, then the interrupt will reassert. For example, consider the following scenario:
1. IS7816[WT] is programmed to assert after 9600 cycles of unresponsiveness.
2. The 9600 cycles pass without a response resulting in the WT interrupt asserting.
3. The IS7816[WT] is cleared at cycle 9700 by the interrupt service routine.
4. After the WT interrupt has been cleared, the smartcard remains unresponsive. At
cycle 9701 the WT interrupt will be reasserted.
If the intent of clearing the interrupt is such that it does not reassert, the interrupt service
routine must remove or clear the condition that originally caused the interrupt to assert
prior to clearing the interrupt. There are multiple ways that this can be accomplished,
including ensuring that an event that results in the wait timer resetting occurs, such as, the
transmission of another packet.
38.9.7 Legacy and reverse compatibility considerations
Recent versions of the UART have added several new features. Whenever reasonably
possible, reverse compatibility was maintained. However, in some cases this was either
not feasible or the behavior was deemed as not intended. This section describes several
differences to legacy operation that resulted from these recent enhancements. If
Application information
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
742
Freescale Semiconductor, Inc.
Содержание MKL27Z128VFM4
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