Rohm LAPIS SEMICONDUCTOR ML620Q503, User Manual

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ML620Q503/Q504 User's Manual
Chapter 14 UART with FIFO(UARTF)
FEUL620Q504 14-16
14.3 Description of Operation
The UART is programmed with UAF0IER, UAF0MOD, DLR(UAF0BUF), and UAF0CAJ. These registers
define the character length, number of stop bits, parity, baud rate, etc.
Though the registers can be written in any order, UAF0IER needs to be written to last because it controls the
interrupt enable. Once the UART is programmed to be operable, these registers can be updated any time when
the UART is not transmitting or receiving data.
14.3.1 Data Transmission
Figure 14-2 shows the transmission timing.
Writing data to THR will transfer the contents through the transmit FIFO to the transmit shift register. Within 16
baud rate clocks after the THRE bit rise is detected, the start bit is sent, followed by the data one bit at a time
from the least significant bit. When the data to be transmitted is 7-bit, the most significant bit will not be sent.
If parity is enabled by UF0PT2-0 of UAF0MOD, then the parity bit is sent. This is followed by the stop bit which
indicates the end of transmitting one frame of data.
After the data is transmitted, the UF0THRE bit of UAF0LSR is set to "1" to indicate that it is ready for the next
transmission. This bit is cleared when one byte is written to the transmit FIFO. Also, if the THRE interrupt is
enabled by UF0ETBEI of UAF0IER, THRE initiates a LVL=3 interrupt to UAF0IIR. If THRE is the interrupt
source indicated in UAF0IR, this bit is cleared by reading the UAF0IIR register.
TXDF0 Start Data bit (5
～
8) Parity Stop Start
(1or2)
tIRS tSTI
UAF0INT
(THRE)
tSI
WR(THR)
RD
IIR Read
tIRS: <16 Baud rate Clocks
tSI: 8
～
16 Baud rate Clocks
tSTI: 8 Baud rate Clocks
Figure 14-2 Transmission Timing
[Note]
Transmit FIFO is an empty state, but there is the case that all transmit processing doesn’t complete.
Confirm that transmit shift register (TSR) became empty in UF0TEMT bit of UAF0LSR register before
stopping high-speed clock (Transition to modes such as STOP / DEEP-HALT / HALT-H).