MC68HC16Z1 Datasheet, PDF (239/500 Pages) Freescale Semiconductor, Inc – M68HC16Z Series

Freescale Semiconductor, Inc.
RDRF must be cleared before the next transfer from the shifter can take place. If
RDRF is set when the shifter is full, transfers are inhibited and the overrun error (OR)
flag in SCSR is set. OR indicates that RDR needs to be serviced faster. When OR is
set, the data in RDR is preserved, but the data in the serial shifter is lost. Because
framing, noise, and parity errors are detected while data is in the serial shifter, FE, NF,
and PF cannot occur at the same time as OR.
When the CPU16 reads SCSR and SCDR in sequence, it acquires status and data,
and also clears the status flags. Reading SCSR acquires status and arms the clearing
mechanism. Reading SCDR acquires data and clears SCSR.
When RIE in SCCR1 is set, an interrupt request is generated whenever RDRF is set.
Because receiver status flags are set at the same time as RDRF, they do not have
separate interrupt enables.
9.4.3.7 Idle-Line Detection
During a typical serial transmission, frames are transmitted isochronally and no idle
time occurs between frames. Even when all the data bits in a frame are logic ones, the
start bit provides one logic zero bit-time during the frame. An idle line is a sequence of
contiguous ones equal to the current frame size. Frame size is determined by the state
of the M bit in SCCR1.
The SCI receiver has both short and long idle-line detection capability. Idle-line detec-
tion is always enabled. The idle line type (ILT) bit in SCCR1 determines which type of
detection is used. When an idle line condition is detected, the IDLE flag in SCSR is set.
For short idle-line detection, the receiver bit processor counts contiguous logic one bit-
times whenever they occur. Short detection provides the earliest possible recognition
of an idle line condition, because the stop bit and contiguous logic ones before and
after it are counted. For long idle-line detection, the receiver counts logic ones after
the stop bit is received. Only a complete idle frame causes the IDLE flag to be set.
In some applications, software overhead can cause a bit-time of logic level one to oc-
cur between frames. This bit-time does not affect content, but if it occurs after a frame
of ones when short detection is enabled, the receiver flags an idle line.
When the ILIE bit in SCCR1 is set, an interrupt request is generated when the IDLE
flag is set. The flag is cleared by reading SCSR and SCDR in sequence. IDLE is not
set again until after at least one frame has been received (RDRF = 1). This prevents
an extended idle interval from causing more than one interrupt.
9.4.3.8 Receiver Wake-Up
The receiver wake-up function allows a transmitting device to direct a transmission to
a single receiver or to a group of receivers by sending an address frame at the start of
a message. Hardware activates each receiver in a system under certain conditions.
Resident software must process address information and enable or disable receiver
operation.
M68HC16 Z SERIES
USER’S MANUAL
QUEUED SERIAL MODULE
For More Information On This Product,
Go to: www.freescale.com
9-29