IA8044 Datasheet, PDF (35/49 Pages) InnovASIC, Inc – SDLC COMMUNICATIONS CONTROLLER

IA8044/IA8344
SDLC COMMUNICATIONS CONTROLLER
Data Sheet
Frame Format Options
The various frame formats available with the IA8044/IA8344 are the standard SDLC format, the no
control field format, the no control field and no address field format and the no FCS field format.
The standard SDLC format consists of an opening flag, an 8-bit address field, an 8-bit control field,
and n-byte information field, a 16-bit frame check sequence field and a closing flag. The FCS is
generated by the CCIT-CRC polynomial (X16 +X12 + X5 + 1). The FCS is calculated on the
address, control and information fields. The address and control fields may not be extended. The
address is contained in STAD and the control filed is contained in either RCB or TCB. This format
is supported by both AUTO and FLEXIBLE modes.
The no control field format is only supported by the FLEXIBLE mode. In this format TCB and
RCB are not used and the information field starts immediately after the address field. A control
field may still be used in the frame but the SIU will treat it as a byte of the information field.
The no control field and no address field format is only supported by the FLEXIBLE mode. In this
format STAD, TCB and RCB are not used and the information field starts immediately after the
opening flag. This option can only be used with the no control field option. Again a control field
and address field may still be used in the frame but the SIU will treat each as a byte of the
information field.
The no FCS field format prevents an FCS from being generated during transmission or being
checked during reception. This option may be used in conjunction with the other frame format
options. This option will work with both FLEXIBLE and AUTO modes. In AUTO mode it could
cause protocol violations. An FCS field may still be used in the frame but the SIU will treat it as a
byte of the information field.
All the possible Frame Format combinations are shown in the table below along with the bit settings
that select a given format.
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