Serial Management Controllers (SMCs)
7-288
MC68360 USER’S MANUAL
MOTOROLA
Data Length
The data length is the number of octets that the CP should transmit from this BD’s data
buffer. It is never modified by the CP. This value should normally be greater than zero.
The data length may be equal to zero with the P-bit set, and only a preamble will be sent.
If the number of data bits in the UART character is greater than 8, then the data length
should be even. Example: to transmit three UART characters of 8-bit data, 1 start, and 1
stop, the data length field should be initialized to 3. However, to transmit three UART char-
acters of 9-bit data, 1 start, and 1 stop, the data length field should be initialized to 6, since
the three 9-bit data fields occupy three words in memory (the 9 LSBs of each word).
Tx Data Buffer Pointer
The transmit buffer pointer, which always points to the first location of the associated data
buffer, may be even or odd (unless the number of actual data bits in the UART character
is greater than 8 bits, in which case the transmit buffer pointer must be even.) For in-
stance, the pointer to 8-bit data, 1 start, and 1 stop characters may be even or odd, but
the pointer to 9-bit data, 1 start, and 1 stop characters must be even. The buffer may re-
side in either internal or external memory.
7.11.7.14 SMC UART EVENT REGISTER (SMCE).
When the UART protocol is selected,
the SMCE register is called the SMC UART event register. It is an 8-bit register used to
report events recognized by the SMC UART channel and to generate interrupts. On recog-
nition of an event, the UART will set the corresponding bit in the SMC UART event register.
The SMC UART 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 clear the
internal interrupt request. This register is cleared at reset.
An example of the timing of various events in the SMC UART event register is shown in Fig-
ure 7-77.
NOTES:
1: Only available on REV C mask or later. NOT Available on REV A or B.
Rev A mask is C63T
Rev B mask are C69T, and F35G
Current Rev C mask are E63C, E68C and F15W
7
—
6
5
—
4
3
—
2
1
0
BRKe
1
BRK
BSY
TX
RX