The frame is transferred to the receive buffer, and S1[RDRF] is set, only if the
comparison matches. All subsequent frames received with a logic 0 in the bit position of
the address mark are considered to be data associated with the address and are transferred
to the receive data buffer. If no marked address match occurs, then no transfer is made to
the receive data buffer, and all following frames with logic 0 in the bit position of the
address mark are also discarded. If both C4[MAEN1] and C4[MAEN2] are negated, the
receiver operates normally and all data received is transferred to the receive data buffer.
Match address operation functions in the same way for both MA1 and MA2 registers.
Note that the position of the address mark is the same as the Parity Bit when parity is
enabled for 8 bit and 9 bit data formats.
• If only one of C4[MAEN1] and C4[MAEN2] is asserted, a marked address is
compared only with the associated match register and data is transferred to the
receive data buffer only on a match.
• If C4[MAEN1] and C4[MAEN2] are asserted, a marked address is compared with
both match registers and data is transferred only on a match with either register.
Address match operation is not supported when C7816[ISO_7816E] is set/enabled.
46.4.3 Baud rate generation
A 13-bit modulus counter and a 5-bit fractional fine-adjust counter in the baud rate
generator derive the baud rate for both the receiver and the transmitter. The value from 1
to 8191 written to SBR[12:0] determines the module clock divisor. The SBR bits are in
the UART baud rate registers, BDH and BDL. The baud rate clock is synchronized with
the module clock and drives the receiver. The fractional fine-adjust counter adds
fractional delays to the baud rate clock to allow fine trimming of the baud rate to match
the system baud rate. The transmitter is driven by the baud rate clock divided by 16. The
receiver has an acquisition rate of 16 samples per bit time.
Baud rate generation is subject to two sources of error:
• Integer division of the module clock may not give the exact target frequency. This
error can be reduced with the fine-adjust counter.
• Synchronization with the module clock can cause phase shift.
The
lists the available baud divisor fine adjust values.
UART baud rate = UART module clock / (16 × (SBR[12:0] + BRFD))
Chapter 46 Universal Asynchronous Receiver/Transmitter (UART)
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
Freescale Semiconductor, Inc.
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