Table of Contents
Advertisement
SCI Queue Operation
• Available transmit wrap function to prevent message breaks for transmits greater
than 16. This is achieved by the transmit wrap enable (QTWE) bit. When QTWE is
set, the hardware is allowed to restart transmitting from the top of the queue
(SCTQ[0]). After each wrap, QTWE is cleared by hardware.
— Transmissions of more than 16 data frames must be performed in multiples of 16
(QTSZ = 0b1111) except for the last set of transmissions. For any single
non-continuous transmissions of 16 or less or the last transmit set composed of
16 or fewer data frames, programming of QTSZ to the corresponding value of 16
or less where QTWE = 0 is allowed.
• Interrupt generation when the top half (SCTQ[0:7]) of the queue has been emptied
(QTHE) and the bottom half (SCTQ[8:15]) of the queue has been emptied (QBHE).
This may allow for uninterrupted and continuous transmits by indicating to the CPU
that it can begin refilling the queue portion that is now emptied.
— The QTHE bit is set by hardware when the top half is empty or the transmission
has completed. The QTHE bit is cleared when the QSCI1SR is read with QTHE
set, followed by a write of QTHE to zero.
— The QBHE bit is set by hardware when the bottom half is empty or the
transmission has completed. The QBHE bit is cleared when the QSCI1SR is read
with QBHE set, followed by a write of QBHE to zero.
— In order to implement the transmit queue, QTE must be set (QSCI1CR), TE must
be set (SCC1R1), QTHE must be cleared (QSCI1SR), and TDRE must be set
(SC1SR).
• Enable and disable options for the interrupts QTHE and QBHE as controlled by
QTHEI and QBHEI respectfully.
• Programmable 4-bit register queue transmit size (QTSZ) for configuring the queue
to any size up to 16 transfers at a time. This value may be rewritten after
transmission has started to allow for the wrap feature.
• 4-bit status register to indicate the number of data transfers pending (QPEND). This
register counts down to all 0's where the next count rolls over to all 1's. This counter
is writable in test mode; otherwise it is read-only.
• 4-bit counter (QTPNT) is used as a pointer to indicate the next data frame within the
transmit queue to be loaded into the SC1DR. This counter is writable in test mode;
otherwise it is read-only.
• A transmit complete (TC) bit re-defined when the queue is enabled (QTE = 1) to
indicate when the entire queue (including when wrapped) is finished transmitting.
This is indicated when QPEND = 1111 and the shifter has completed shifting data
out. TC is cleared when the SCxSR is read with TC = 1 followed by a write to
SCTQ[0:15]. If the queue is disabled (QTE = 0), the TC bit operates as originally
designed.
• When the transmit queue is enabled (QTE = 1), writes to the transmit data register
(SC1DR) have no effect.
15-68
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
MPC533 Reference Manual
MOTOROLA
Advertisement
Table of Contents
