MOTOROLA
Chapter 24. SCC HDLC Mode
24-11
Part V. The Communications Processor Module
24.10 SCC HDLC Transmit Buffer Descriptor (TxBD)
The CPM uses the TxBD, shown in Figure 24-7, to conÞrm transmissions and indicate error
conditions.
Table 24-8 describes HDLC TxBD status and control Þelds.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
R
Ñ
W
I
L
TC
CM
Ñ
UN
CT
2
Data Length
4
Tx Buffer Pointer
6
Figure 24-7. SCC HDLC Transmit Buffer Descriptor (TxBD)
Table 24-8. SCC HDLC TxBD Status and Control Field Descriptions
Bits
Name
Description
0
R
Ready.
0 The buffer is not ready for transmission. Both the buffer and the BD can be updated. The CPM
clears R after the buffer is sent or an error is encountered.
1 The buffer has not been sent or is being sent and the BD cannot be updated.
1
Ñ
Reserved, should be cleared.
2
W
Wrap (last BD in TxBD table).
0 Not the last BD in the table.
1 Last BD in the BD table. After this buffer is used, the CPM sends data using the BD pointed to by
TBASE. The number of TxBDs in this table is determined by TxBD[W] and the space constraints of
the dual-port RAM.
3
I
Interrupt.
0 No interrupt is generated after this buffer is processed.
1 SCCE[TXB] or SCCE[TXE] is set when this buffer is processed, causing interrupts if not masked.
4
L
Last.
0 Not the last buffer in the frame.
1 Last buffer in the frame.
5
TC
Tx CRC. Valid only when TxBD[L] = 1. Otherwise, it is ignored.
0 Transmit the closing ßag after the last data byte. This setting can be used to send a bad CRC after
the data for testing purposes.
1 Transmit the CRC sequence after the last data byte.
6
CM
Continuous mode.
0 Normal operation.
1 The CP does not clear TxBD[R] after this BD is closed allowing the buffer to be resent the next time
the CP accesses this BD. However, TxBD[R] is cleared if an error occurs during transmission,
regardless of CM.
7Ð13 Ñ
Reserved, should be cleared.
14
UN
Underrun. Set after the SCC sends a buffer and a transmitter underrun occurred.
15
CT
CTS lost. Indicates when CTS in NMSI mode or layer 1 grant is lost in GCI or IDL mode during frame
transmission. If data from more than one buffer is currently in the FIFO when this error occurs, the
HDLC writes CT in the current BD after sending the buffer.
Summary of Contents for MPC860 PowerQUICC
Page 3: ...MPC860UM AD 07 98 REV 1 MPC860 PowerQUICC ª UserÕs Manual ...
Page 36: ...xxxvi MPC860 PowerQUICC UserÕs Manual MOTOROLA CONTENTS Paragraph Number Title Page Number ...
Page 78: ...I iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 88: ...1 10 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 114: ...3 16 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 226: ...8 32 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part II PowerPC Microprocessor Module ...
Page 262: ...9 36 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part II PowerPC Microprocessor Module ...
Page 274: ...III iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
Page 320: ...12 12 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
Page 325: ...MOTOROLA Part IV Hardware Interface IV v Part IV Hardware Interface ...
Page 326: ...IV vi MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
Page 352: ...13 26 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
Page 394: ...14 42 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
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Page 632: ...21 44 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 660: ...22 28 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
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Page 998: ...37 48 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part VI Debug and Test ...
Page 1016: ...A 10 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
Page 1024: ...B 8 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
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