mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 1133

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Chapter 43 Universal Asynchronous Receiver/Transmitter (UART)
43.8.5 Overrun NACK considerations
When C7816[ISO_7816E] is enabled and C7816[TTYPE] = 0 the retransmission feature
of the 7816 protocol can be used to help avoid lost data when the data buffer overflows.
Using C7816[ONACK] the module can be programmed to issue a NACK on an overflow
event. Assuming that the device (smartcard) has implemented retransmission, the lost
data will be retransmitted. While useful, there is a programming implication which may
require special consideration. The need to transmit a NACK must be determined and
committed to prior to the dataword being fully received. While the NACK is being
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 once 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 the S1[OR] flag will be
blocked and kept from asserting.
43.8.6 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.
43.8.7 Modem feature
This section describes the modem features.
43.8.7.1 Ready-to-receive using RTS
To help to stop overrun of the receiver data buffer, the RTS signal can be used by the
receiver to indicate to another UART that it is ready to receive data. The other UART can
send the data when its CTS signal is asserted. This handshaking conforms to the
TIA-232-E standard. A transceiver is necessary if the required voltage levels of the
communication link do not match the voltage levels of the UART's RTS and CTS signals.
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Preliminary
Freescale Semiconductor, Inc.
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