MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 461

• Manufacturer Part Number: MC68000
• Manufacturer: MOTOROLA [Motorola, Inc]

E—Empty
X—External Buffer
W—Wrap (final BD in table)
I—Interrupt
Bits 11-2—Reserved for future use; should be written with zero by the user.
OV—Overrun
CD—Carrier Detect Lost (valid only in NMSI mode)
E.3.1.4.2 Receive Buffer Data Length. This 16-bit value is written by the lMP to indicate
the number of data bytes received into the data buffer.
E.3.1.4.3 Receive Buffer Pointer. This 32 bit value is written by the user to indicate the
address where the data is to be stored.
E.3.1.5 TRANSMIT BUFFER DESCRIPTORS. Each SCC has eight transmit buffer
descriptors. Each buffer descriptor consists of four words as shown below. Reserved bits in
registers should be written as zeros.
E.3.1.5.1 Transmit BD Control/Status Word. To initialize the buffer, the user should write
bits 15-11 and clear bits 1-0. The IMP clears bit 15 when the buffer is transmitted or closed
due to an error and sets bits 1-0 depending on which error occurred.
MOTOROLA
OFFSET + 0
OFFSET +2
OFFSET +4
OFFSET +6
0 = This data buffer is full or has been closed due to an error condition.
1 = This data buffer is empty; must be set by the user to enable reception into this buff-
0 = The data buffer associated with this BD is in internal dual-port RAM.
1 = The data buffer associated with this BD is in external memory.
0 = This is not the last BD in the receive BD table.
1 = This is the last BD in the receive BD table.
0 = No interrupt is generated when this buffer is closed.
1 = The RX bit in the event register is set when this buffer is closed.
0 = No receiver overrun occurred.
1 = A receiver overrun condition occurred during frame reception.
0 = No CD lost was detected.
1 = CD was negated during frame reception.
er.
15
R
14
X
13
W
12
I
11
L
MC68360 USER’S MANUAL
10
—
—
9
TX BUFFER POINTER
DATA LENGTH
—
8
—
7
—
6
—
5
SCC Programming Reference
—
4
—
3
—
2
UN
1
E-39
CT
0