xerox 19770728 D0 RS232C Controller Functional Specifications free download

File name 19770728_D0_RS232C_Controller_Functional_Specifications.pdf

Internal Memorandum To Distribution Date July 28, 1977 From Victor Schwartz and Roy Ogus Location Palo Alto Subject DO RS232C Controller Organization SOO/SO/CS Functional Specifications XEROX SDD ARCHIVES XEROX I have read and understood Pages _________To _________ Reviewer Date _ _ __ Filed on: [MAXC]Control\er-memo.press I of Pagee Ref .,1;7~DD- Z'7t Introduction This memo specifies the functions performed by the DO RS232C Controller, and how PILOT software interfaces to the controller microcode in order to control these functions. Controller Status Block Software and microcode communicate via Controller Status Blocks (CSBs) located at dedicated memory addresses. There are separate CSBs for input and output (although implementation may assign them contiguous), since the support of full-duplex links requires the microcode to treat input and output as separate channels. The CSB contains various flags (see Table Formats below), and a pointer to a chain of Input/Output Control Blocks (IOCBs). Input/Output Control Block The IOCB is the structure by which the software passes a single command to the controller microcode. Parameters within the IOCB describe the function to be performed, the resulting status, and the data areas involved. IOCBs are chained together by PILOT software, and are processed sequentially by the microcode. Each IOCB instructs the microcode as to which process wakeups to perform and when. Each processed IOCB is flagged by the microcode, and later dequeued by the software. Command Five commands are described by the command field in the IOCB. They are: 1. Reset 2. Change parameter 3. Transmit/Receive frame 4. Transmit break (asynchronous lines only) 5. Dial-a-Digit Frames A frame is the smallest meaningful unit of transmission across the communication link. The format and content of a frame depend upon the link control protocol, and are described in Frame Formats below, for each of the link control protocols supported by the DO RS232C Controller. Frames are stored into frame buffers allocated by software. A single frame may be split across non-contiguous buffers to allow scatter/gather facilities, although no buffer contains more than one frame.