IA8044/IA8344
SDLC COMMUNICATIONS CONTROLLER
Preliminary Data Sheet
As of Production Version 00
Operational Modes
The SIU operates in one of two modes, AUTO or FLEXIBLE. The mode selected determines
how much intervention is required by the CPU when receiving frames. In both modes short
frames, aborted frames, and frames with CRC errors will be ignored.
AUTO mode allows the SIU to recognize and respond to specific SDLC frames without the CPUs
intervention. This provides for a faster turnaround time but restricts the operation of the SIU.
When in AUTO mode the SIU can only act as a normal response secondary station and responses
will adhere to IBM’s SDLC definitions.
When receiving in the AUTO mode the SIU receives the frame and examines the control byte. It
will then take the appropriate action for that frame. If the frame is an information frame the SIU
will load the receive buffer, interrupt the CPU and make the required response to the primary
station. The SIU in AUTO mode can also respond to the following commands from the primary
station.
RR (Receive ready),
RNR (Receive Not Ready),
REJ (Reject),
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 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.
Copyright
innovASIC
2001
ENG210010112-00
www.innovasic.com
Customer Support:
1-888-824-4184
The End of Obsolescence
Page 21 of 32
INNOVASIC [ INNOVASIC, INC ]
