IA8044/IA8344
Data Sheet
SDLC Communications Controller
March 30, 2010
UP (Unnumbered Poll) also called NSP, (Non-Sequenced Poll), or ORP (Optional
Response Poll)
In AUTO mode when the transmit buffer is full, the SIU can transmit an information frame when
polled for information. After transmission the SIU waits for acknowledgement from the receiving
station. If the response is positive, the SIU interrupts the CPU. If the response is negative, the
SIU retransmits the frame. The SIU can send the following responses to the primary station:
RR (Receive Ready)
RNR (Receive Not Ready)
The FLEXIBLE mode requires the CPU to control the SIU for both transmitting and receiving.
This slows response time but allows full SDLC and limited HDLC compatibility as well as
variations. In FLEXIBLE mode, the SIU can act as a primary station. The SIU will interrupt the
CPU after completion of a transmission without waiting for a positive acknowledgement from the
receiving station (see Table 46).
Table 46. Basic SDLC Frame
FLAG ADDRESS CONTROL INFORMATION FCS FLAG
IA8044/IA8344 frame parameters:
Flag—8 bits
Address—8 bits
Control—8 bits
Information—n bytes (where n 192)
FCS—16 bits
Flag—8 bits
4.13 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 formats, 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, an 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.
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