MK50H25 查看數據表（PDF） - STMicroelectronics
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MK50H25 Datasheet PDF : 62 Pages
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scriptor ring in a "look ahead" manner. If the
frame is too long for one buffer, the next buffer
will be used after filling the first buffer; that is,
"chained". The MK50H25 will then "look ahead"
to the next buffer, and chain that buffer if neces-
sary, and so on.The operational parameters for
the buffer management are defined by the user in
the initialization block. The parameters defined
include the basic mode of operation, the number
of entries for the transmitter and receiver descrip-
tor rings, frame Address field, etc. The starting
address for the Initialization block, IADR, is de-
fined in the CSR2 and CSR3 registers inside the
MK50H25.
3.2.3 Frame Format
The frame format supported by the MK50H25 is
shown below. Each frame may consist of a pro-
grammable number of leading flag patterns
(01111110), an address field, a control field, an
information field, an FCS (CRC) of either 16 or 32
bits, and a trailing flag pattern. The number of
leading flags transmitted is programmable
through the Mode Register in the Initialization
Block. Received frames may have as few as one
flag between adjacent frames
TRANSMITTED FIRST
F
A
C
8
8/16 8/16
INFO
8*n
FCS
F
16/32
8
MK50H25
3.2.4 The Command/Response Repertoire
The command/response repertoire of the
MK50H25 is shown in Tables A and B. This set
conforms to the 1984 & 1988 CCITT X.25, plus
support of XID, Test, and UI frames conforming to
ISDN LAPD. The MK50H25 will process the In-
formation, Supervisory, and Unnumbered frames
shown in Tables A and B, and will handle the A
and C fields for all I and UI frames.
The symbols and definitions for the frame types
are:
Name
I
UI
RR
RNR
REJ
FRMR
UA
SABM
DISC
DM
TEST
XID
Definition
Information frame
Unnumbered Information frame
Receiver Ready
Receiver Not Ready
Reject
Frame Reject
Unnumbered Acknowledge
Set Asynchronous Balance Mode
Disconnect
Disconnect Mode
Link Test Frame
Exchange Identification
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