
Communications Processor (CP)
MOTOROLA
MC68302 USER’S MANUAL
4-133
Data Length
The data length is the number of octets that the CP should transmit from this BD's data
buffer. The data length, which should be greater than zero, may be even or odd. This val-
ue is never modified by the CP.
Tx Buffer Pointer
The transmit buffer pointer, which always points to the first byte of the associated data
buffer, may be even or odd. The buffer may reside in either internal or external memory.
NOTE
For correct operation of the function codes, the upper 8 bits of
the pointer must be initialized to zero.
4.5.16.10 Transparent Event Register
The SCC event register (SCCE) is referred to as the transparent event register when the
SCC is programmed as a transparent controller. It is an 8-bit register used to report events
recognized by the transparent channel and to generate interrupts. On recognition of an
event, the transparent controller sets the corresponding bit in the transparent event register.
Interrupts generated by this register may be masked in the transparent mask register.
The transparent event register is a memory-mapped register that may be read at any time.
A bit is cleared by writing a one (writing a zero does not affect a bit's value). More than one
bit may be cleared at a time. All unmasked bits must be cleared before the CP will negate
the internal interrupt request signal. This register is cleared at reset.
CTS—Clear-To-Send Status Changed
A change in the status of the serial line was detected on the transparent channel. The
SCC status register may be read to determine the current status.
CD—Carrier Detect Status Changed
A change in the status of the serial line was detected on the transparent channel. The
SCC status register may be read to determine the current status.
Bit 5—Reserved for future use.
TXE—Tx Error
An error (CTS lost or underrun) occurred on the transmitter channel.
RCH—Receive Character
A word has been received and written to the receive buffer.
BSY—Busy Condition
A word was received and discarded due to lack of buffers. The receiver will resume re-
ception after an ENTER HUNT MODE command.
7
6
5
4
3
2
1
0
CTS
CD
—
TXE
RCH
BSY
TX
RX