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ting the number of data records to be read from the Metrodata tape reader, are performed. Each record on the tape contains the data for all 20 channels. Next, subroutine ZPRTY is called to set the various flags used by the Metrodata tape driver subroutine (METRO) and its associated subroutines. Then, the METRO driver is called to transfer the designated number of data records into the buffer section of core memory. To avoid destroying any Input/Output operation that may be in progress, METRO first enters a wait loop until the BCS input/output control (.IOC.) subroutine returns an I/O status showing that no I/O is in progress. At this point, METRO establishes the necessary addresses and counters and finally sends the reset and start commands to the tape reader. Since each data scan on the magnetic tape has 80 data characters (20 data channels X 4 characters/channel) plus preparity and parity characters for a total of 82 4-bit characters, the METRO driver starts to search for a preparity character. When METRO finds a preparity character (either X ' C or X'D'), it counts ahead 82 4-bit bytes to check if the 82nd byte is also a preparity character. If this 82nd byte is indeed a preparity character, METRO goes back to the beginning of the pertinent record and checks the second 4-bit byte of this record to ensure that it is a plus or minus character. If not, the preparity search procedure is repeated until a proper data record is located or an end-of-tape (EOT) condition is encountered. After successfully finding a second preparity character at the 82nd byte and a sign character in the second byte, METRO transfers the 20 channels of data in the respective record to the buffer memory of the minicomputer. As the 4-byte information in each channel is read from the tape, the corresponding 4-bit BCD data are converted to 2's-complement by METRO and subsequently stored in consecutive words of buffer memory. If METRO encounters an end-of-tape at any time during the buffer loading procedure, program control is returned to GETRC. GETRC then notes the number of records that were stored in the buffer prior to the EOT signal for later use in the processing and averaging algorithms. Both the EOT condition and the number of data scans used in the specified calculations are output to alert the operator. The preceding sequence continues until either the buffer is filled with the designated number of data scans or an EOT is detected. After these functions, GETRC starts to read individual scans from the buffer created by METRO until
CIRCLE 98 ON READER SERVICE CARD
366 A · ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
Analytical Methods in Oceanography Advances in Chemistry Series No. 147 Thomas R. P. Gibb, Jr., Editor A symposium sponsored by the Division of Analytical Chemistry of the American Chemical Society. A significant volume providing the marine chemist with the newest tools for detecting and monitoring ocean contamination—a problem of ever-growing proportions. This valuable resource advances the task of problem solving by equipping the shore-based chemist with the latest sampling and analysis skills developed by the marine chemist. Discussion of current techniques, contaminants, and situations makes this collection necessary reading for marine and analytical chemists alike. Eighteen chapters describe recent developments in: in situ sampling and concentration, APDC chelate co-precipitation, flameless atomic absorption spectroscopy, automated anodic stripping voltammetry, cold trap pre-concentration, gas phase detection, gas chromatographic-mass spectrometry, and others. 238 pages (1975) Clothbound $26.50 (ISBN 0-8412-0245-1) LC 75-41463
SIS/American Chemical Society 1155 16th St., N.W./Wash., D.C. 20036 Please send copies of No. 147 Analytical Methods in Oceanography at $26.50 per book. D Check is enclosed for $ D Bill me. Postpaid in U.S. and Canada, plus 40 cents elsewhere. Name Address City
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