28500-DSH-002-C_15 Datasheet, PDF (129/224 Pages) M/A-COM Technology Solutions, Inc. – Multichannel Synchronous Communications Controller

Memory Organization
Table 6-40. Transmit Buffer Descriptor (2 of 2)
Bit
Field Name
Value
Description
29
EOM
0
End Of Message Indicator clear—this is not the last buffer for the current message.
1
End Of Message Indicator set—this is the last buffer for the current message.
28
EOBIEN
0
End Of Buffer Interrupt Disabled. When the last data byte was taken from this buffer, an EOB interrupt
is not generated.
27:26
IC[1:0]⁽¹⁾
1
End Of Buffer Interrupt Enabled. When the last data byte was taken from this buffer, or the BSD is
written, an EOB interrupt is generated.
0
Idle Code Select—If the protocol is HDLC, the Idle Code Select is 7Eh. If the protocol is transparent,
the Idle Code Select is FFh.
1
Idle Code Select—If the protocol is HDLC, the Idle Code Select is FFh. If the protocol selection is
transparent, the Idle Code Select is 7Eh.
2
Idle Code Select—00h.
25:18
PADCNT[7:0]⁽²⁾
RSVD [7:0]
3
Reserved.
— Pad Count/Reserved.
When operating in normal mode (i.e., not in Preserve Channel Mode) this field is treated as
PADCOUNT. PADCNT indicates the minimum number of idle codes to be inserted between the closing
flags and the next opening flag (7Eh). If PADCNT = 2 and IC = 1, for example, CX28500 outputs the bit
pattern 7Eh..FFh..FFh..7Eh. There is no indication by CX28500 if more than PADCNT number of idle
codes are inserted. When operating in Preserve Channel Mode, this field is treated as a reserved field
whose bits are preserved in the Transmit Buffer Descriptor.
17:15
ABORT
0
Packet should be transmitted and end correctly.
1-7 Packet transmission should end with ABORT sequence when EOM = 1.
14
TxLAST
0
This is not the last MD in this message descriptor table.
1
This is the last MD in this message descriptor table.
13:0
BLEN[13:0]⁽³⁾
— Buffer Length. The number of bytes in data buffer to be transmitted. In general, this would equal the
allocated buffer size. If EOM = 0 and BLEN = 0, the DMA ignores this BD and skips to the next one. If
EOM = 1, BLEN = 0, ABORT = 0, and prior NOT-EOM data buffer, the DMA completes transmission of
the prior buffer.
FOOTNOTE:
(1) _{IC field is processed and used by CX28500 only when EOM is set (i.e., only in the last buffer descriptor of a message).}
(2) _{PADCNT field is processed and used by CX28500 only when EOM is set (i.e., only in the last buffer descriptor of a message).}
(3) _{The combination of BLEN = 0 and EOM = 0 in the middle of a message is not allowed.}
Table 6-41. Receive Buffer Descriptor (1 of 2)
Bit
Field Name
Value
Description
31
ONR
0
CX28500 Owns Buffer. Continue processing data buffer normally.
1
HOST Owns Buffer. Channel is to remain in idle mode while polling this bit periodically (if NP = 0) until
Host relinquishes control to CX28500 by setting ONR = 0.
30
NP
0
Poll Enabled. If ONR = 1, Host-owned, CX28500 polls message descriptor periodically until ONR = 0.
1
Poll Disabled. If ONR = 1, then enter suspend mode and wait for a Channel Activate or Jump Host
Service from Host.
29
RSVD
0
Reserved.
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