MC68HC908GZ8 Datasheet, PDF (225/344 Pages) Motorola, Inc – Microcontrollers

Enhanced Serial Communications Interface (ESCI) Module
Functional Description
bit automatically goes into the least significant bit (LSB) position of the transmit shift
register. A logic 1 stop bit goes into the most significant bit (MSB) position.
The ESCI transmitter empty bit, SCTE, in SCS1 becomes set when the SCDR
transfers a byte to the transmit shift register. The SCTE bit indicates that the SCDR
can accept new data from the internal data bus. If the ESCI transmit interrupt
enable bit, SCTIE, in SCC2 is also set, the SCTE bit generates a transmitter CPU
interrupt request.
When the transmit shift register is not transmitting a character, the TxD pin goes to
the idle condition, logic 1. If at any time software clears the ENSCI bit in ESCI
control register 1 (SCC1), the transmitter and receiver relinquish control of the port
E pins.
19.4.2.3 Break Characters
Writing a logic 1 to the send break bit, SBK, in SCC2 loads the transmit shift
register with a break character. For TXINV = 0 (output not inverted), a transmitted
break character contains all logic 0s and has no start, stop, or parity bit. Break
character length depends on the M bit in SCC1 and the LINR bits in SCBR. As long
as SBK is at logic 1, transmitter logic continuously loads break characters into the
transmit shift register. After software clears the SBK bit, the shift register finishes
transmitting the last break character and then transmits at least one logic 1. The
automatic logic 1 at the end of a break character guarantees the recognition of the
start bit of the next character.
When LINR is cleared in SCBR, the ESCI recognizes a break character when a
start bit is followed by eight or nine logic 0 data bits and a logic 0 where the stop bit
should be, resulting in a total of 10 or 11 consecutive logic 0 data bits. When LINR
is set in SCBR, the ESCI recognizes a break character when a start bit is followed
by 9 or 10 logic 0 data bits and a logic 0 where the stop bit should be, resulting in
a total of 11 or 12 consecutive logic 0 data bits.
Receiving a break character has these effects on ESCI registers:
• Sets the framing error bit (FE) in SCS1
• Sets the ESCI receiver full bit (SCRF) in SCS1
• Clears the ESCI data register (SCDR)
• Clears the R8 bit in SCC3
• Sets the break flag bit (BKF) in SCS2
• May set the overrun (OR), noise flag (NF), parity error (PE),
or reception in progress flag (RPF) bits
MC68HC908GZ8
Freescale Semiconductor
Enhanced Serial Communications Interface (ESCI) Module
Data Sheet
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