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22.4 Application Information
This section provides examples for a variety of FlexIO module applications.
22.4.1 UART Transmit
UART transmit can be supported using one Timer, one Shifter and one Pin (two Pins if
supporting CTS). The start and stop bit insertion is handled automatically and multiple
transfers can be supported using DMA controller. The timer status flag can be used to
indicate when the stop bit of each word is transmitted.
Break and idle characters require software intervention, before transmitting a break or
idle character the SSTART and SSTOP fields should be altered to transmit the required
state and the data to transmit must equal 0xFF or 0x00. Supporting a second stop bit
requires the stop bit to be inserted into the data stream using software (and increasing the
number of bits to transmit). Note that when performing byte writes to SHIFTBUFn (or
SHIFTBUFBIS for transmitting MSB first), the rest of the register remains unaltered
allowing an address mark bit or additional stop bit to remain undisturbed.
FlexIO does not support automatic insertion of parity bits.
Table 22-4. UART Transmit Configuration
Register
Value
Comments
SHIFTCFGn
0x0000_0032
Configure start bit of 0 and stop bit of 1.
SHIFTCTLn
0x0003_0002
Configure transmit using Timer 0 on
posedge of clock with output data on Pin
0. Can invert output data by setting
PINPOL, or can support open drain by
setting PINPOL=0x1 and PINCFG=0x1.
TIMCMPn
0x0000_0F01
Configure 8-bit transfer with baud rate of
divide by 4 of the FlexIO clock. Set
TIMCMP[15:8] = (number of bits x 2) - 1.
Set TIMCMP[7:0] = (baud rate divider /
2) - 1.
TIMCFGn
0x0000_2222
Configure start bit, stop bit, enable on
trigger low and disable on compare. Can
support CTS by configuring TIMEN=0x3.
TIMCTLn
0x01C0_0001
Configure dual 8-bit counter using
Shifter 0 status flag as inverted internal
trigger source. Can support CTS by
configuring PINSEL=0x1 (for Pin 1) and
PINPOL=0x1.
SHIFTBUFn
Data to transmit
Transmit data can be written to
SHIFTBUF[7:0] to initiate an 8-bit
Chapter 22 Flexible I/O (FlexIO)
K32 L2A Reference Manual, Rev. 2, 01/2020
NXP Semiconductors
575
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