In the case of a framing error, provided the received character was not a break character,
the sampling logic that searches for a falling edge is filled with three logic 1 samples so
that a new start bit can be detected almost immediately.
In the case of a framing error, the receiver is inhibited from receiving any new characters
until the framing error flag is cleared. The receive shift register continues to function, but
a complete character cannot transfer to the receive data buffer if SCI_S1[FE] remains set.
14.4.3.2 Receiver wake-up operation
Receiver wake-up is a hardware mechanism that allows an SCI receiver to ignore the
characters in a message intended for a different SCI receiver. In such a system, all
receivers evaluate the first character(s) of each message, and as soon as they determine
the message is intended for a different receiver, they write logic 1 to the receiver wake up
control field (SCI_C2[RWU]). When SCI_C2[RWU] is set, the status flags associated
with the receiver, (with the exception of the idle bit, IDLE, when SCI_S2[RWUID] is
set), are inhibited from setting, thus eliminating the software overhead for handling the
unimportant message characters. At the end of a message, or at the beginning of the next
message, all receivers automatically force SCI_C2[RWU] to 0, so all receivers wake up
in time to look at the first character(s) of the next message.
14.4.3.2.1 Idle-line wakeup
When wake is cleared, the receiver is configured for idle-line wakeup. In this mode,
SCI_C2[RWU] is cleared automatically when the receiver detects a full character time of
the idle-line level. The SCI_C1[M] control field selects 8-bit or 9-bit data mode and
SCI_BDH[SBNS] selects 1-bit or 2-bit stop bit number that determines how many bit
times of idle are needed to constitute a full character time, 10 or 11 or 12 bit times
because of the start and stop bits.
When SCII_C2[RWU] is 1 and SCI_S2[RWUID] is 0, the idle condition that wakes up
the receiver does not set SCI_S1[IDLE]. The receiver wakes up and waits for the first
data character of the next message that sets SCI_S1[RDRF] and generates an interrupt, if
enabled. When SCI_S2[RWUID] is 1, any idle condition sets SCI_S1[IDLE] flag and
generates an interrupt if enabled, regardless of whether SCI_C2[RWU] is 0 or 1.
The idle-line type (SCI_C1[ILT]) control bit selects one of two ways to detect an idle
line. When SCI_C1[ILT] is cleared, the idle bit counter starts after the start bit so the stop
bit and any logic 1s at the end of a character count toward the full character time of idle.
When SCI_C1[ILT] is set, the idle bit counter does not start until after a stop bit time, so
the idle detection is not affected by the data in the last character of the previous message.
Chapter 14 Serial communications interface (SCI)
MC9S08PA4 Reference Manual, Rev. 5, 08/2017
NXP Semiconductors
287
Содержание MC9S08PA4
Страница 1: ...MC9S08PA4 Reference Manual Supports MC9S08PA4 Document Number MC9S08PA4RM Rev 5 08 2017 ...
Страница 2: ...MC9S08PA4 Reference Manual Rev 5 08 2017 2 NXP Semiconductors ...
Страница 22: ...MC9S08PA4 Reference Manual Rev 5 08 2017 22 NXP Semiconductors ...
Страница 28: ...System clock distribution MC9S08PA4 Reference Manual Rev 5 08 2017 28 NXP Semiconductors ...
Страница 150: ...Port data registers MC9S08PA4 Reference Manual Rev 5 08 2017 150 NXP Semiconductors ...
Страница 196: ...Human machine interfaces HMI MC9S08PA4 Reference Manual Rev 5 08 2017 196 NXP Semiconductors ...
Страница 224: ...Instruction Set Summary MC9S08PA4 Reference Manual Rev 5 08 2017 224 NXP Semiconductors ...
Страница 232: ...Functional Description MC9S08PA4 Reference Manual Rev 5 08 2017 232 NXP Semiconductors ...
Страница 258: ...FTM Interrupts MC9S08PA4 Reference Manual Rev 5 08 2017 258 NXP Semiconductors ...
Страница 268: ...Initialization application information MC9S08PA4 Reference Manual Rev 5 08 2017 268 NXP Semiconductors ...
Страница 294: ...Functional description MC9S08PA4 Reference Manual Rev 5 08 2017 294 NXP Semiconductors ...
Страница 370: ...Memory map and register description MC9S08PA4 Reference Manual Rev 5 08 2017 370 NXP Semiconductors ...
Страница 398: ...Resets MC9S08PA4 Reference Manual Rev 5 08 2017 398 NXP Semiconductors ...
Страница 400: ...MC9S08PA4 Reference Manual Rev 5 08 2017 400 NXP Semiconductors ...