COMPUTER TO TCS ASCII COMMUNICATIONS : Introduction

Jim Harwood

Revised March 17, 1999

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Introduction

Following is a description of the Forth commands issued from a remote computer to cause the TCS to perform certain functions. In all cases, the commands must be in upper case and have arguments delimited by spaces before the command (standard Forth protocol).

These commands may be typed in for testing at either the LSI-11 or at the remote computer in terminal emulation mode. The TCS response to the commands will be exactly the same, whether the commands are issued from a terminal or from a program.

The end-of-stream prompt from the LSI-11 is -OK<cr><nl> . This sequence (without the period) occurs at the end of the transmission from the LSI-11 and will always occur, whether or not other data is transmitted. If an LSI-11 transmission consists of multiple lines, the lines are ended with <cr><nl>.

In this document, ASCII strings returned to the remote computer from the LSI-11 are printed in typewriter style. Actual text is in upper case; lower case italics indicates a general format of the returned data, such as hh:mm:ss.

Ascii strings sent to the LSI-11 are printed here in boldface.

LSI-11 Response Formats:

You may need to know the exact format of the responses returned by the TCS LSI-11. In the examples in this document, the fields of the LSI-11 response are separated by more than one space for clarity. They actually are always separated by only one space. The fields are fixed format with respect to the number of characters in each field and the number of decimal places. For further information, see the author.

IMPORTANT NOTE: Some of these commands have a "wait for motion complete" option. The LSI-11 computer will hold off returning to the remote computer until completion of the instructions to move the telescope. However, the telescope may still be physically moving, since there is an inertial lag in the telescope response. The TCS does not check for this inertial lag. If this is important, you are advised to hold off the next operation for a second or two after the reply comes back from the LSI-11.

Also, use of the "wait for motion complete" may cause the communications link between the remote computer and the TCS to time out, creating a "comproc" (or other) error. The communications link at the remote computer expects the TCS to respond within a second or two to the transmitted command. Use the "wait for motion complete" option with care. In fact, you are advised NOT to wait for motion complete. Either provide a fixed time interval to allow the motion to complete, or loop on a request for status after sending the telescope motion command. See POLL-OFB.