mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 424

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

Serial Communication Interface (SCI)Serial Communications Interface (SCIV4)
interrupts, software polling may be used to monitor the TDRE and TC status flags if the corresponding
TIE or TCIE local interrupt masks are cleared.
When a program detects that the receive data register is full (RDRF = 1), it gets the data from the receive
data register by reading SCIxD. The RDRF flag is cleared by reading SCIxS1 while RDRF is set and then
reading SCIxD.
When polling is used, this sequence is naturally satisfied in the normal course of the user program. If
hardware interrupts are used, SCIxS1 must be read in the interrupt service routine (ISR). Normally, this is
done in the ISR anyway to check for receive errors, so the sequence is automatically satisfied.
The IDLE status flag includes logic that prevents it from getting set repeatedly when the RxD line remains
idle for an extended period of time. IDLE is cleared by reading SCIxS1 while IDLE is set and then reading
SCIxD. After IDLE has been cleared, it cannot become set again until the receiver has received at least
one new character and has set RDRF.
If the associated error was detected in the received character that caused RDRF to be set, the error flags
— noise flag (NF), framing error (FE), and parity error flag (PF) — are set at the same time as RDRF.
These flags are not set in overrun cases.
If RDRF was already set when a new character is ready to be transferred from the receive shifter to the
receive data buffer, the overrun (OR) flag is set instead of the data along with any associated NF, FE, or
PF condition is lost.
At any time, an active edge on the RxD serial data input pin causes the RXEDGIF flag to set. The
RXEDGIF flag is cleared by writing a 1 to it. This function does depend on the receiver being enabled
(RE = 1).
18.3.5
Additional SCI Functions
The following sections describe additional SCI functions.
18.3.5.1
8- and 9-Bit Data Modes
The SCI system (transmitter and receiver) can be configured to operate in 9-bit data mode by setting the
M control bit in SCIxC1. In 9-bit mode, there is a ninth data bit to the left of the msb of the SCI data
register. For the transmit data buffer, this bit is stored in T8 in SCIxC3. For the receiver, the ninth bit is
held in R8 in SCIxC3.
For coherent writes to the transmit data buffer, write to the T8 bit before writing to SCIxD.
If the bit value to be transmitted as the ninth bit of a new character is the same as for the previous character,
it is not necessary to write to T8 again. When data is transferred from the transmit data buffer to the
transmit shifter, the value in T8 is copied at the same time data is transferred from SCIxD to the shifter.
The 9-bit data mode is typically used with parity to allow eight bits of data plus the parity in the ninth bit,
or it is used with address-mark wakeup so the ninth data bit can serve as the wakeup bit. In custom
protocols, the ninth bit can also serve as a software-controlled marker.
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
18-16
Freescale Semiconductor