REWIND TAPE - [

The Rewind Tape instruction, coded [ (left bracket) instructs the Tape Transport selected by the Z Y characters to rewind to the load point.

7.9.4 WRITE FILE MARK-Io

The Write File Mark, coded ~ (EOM character), instructs the Tape Transport selected by the Z Y characters to write a file mark 3 inches from the end of the last record.

Sec tion VIII

SECTION VIII

UNI-RECORD CONSOLES

The Uni-Record Trunkline is the means of Central Processor operation with associ-ated Tape Transports, Card Reader / Punch, and Line Printer. A Uni- Record

Trunkline can accommodate 256 peripheral devices, a device being defined as a tape transport, a Card Reader/Punch or Line Printer. Each of these devices is con-trolled through the Magnetic Tape Console, which contains Tape Transport, Card Reader / Punch, and Line Printer Control Sections.

The Magnetic Tape Console contains logic, control, and data circuits for each Tape Transport and peripheral device necessary to perform on-line and off-line

functions: on-line functions under Central Processor program control and off-line under manual control. Major functions of the Magnetic Tape Console are:

a. Transferring of programs and data from magnetic tape or cards into Core Memory (on-line).

b. Transferring of data and programs between magnetic tape and cards (off-line).

c. Controlling of data transfer between cards and line printer (off-line).

d. Transferring of data from magnetic tape to line printer (off-line).

e. Transferring of data from Core Memory to magnetic tape or cards under program control (on-line).

£. Transferring of data from core memory to line printer (on-line).

For on-line operation, the Central Proces sor program may select either one of two Tape Transports to send or receive data fr.om the Core Memory, via the Uni-Record Trunkline; however, only one Tape Transport may be operated on-line at a given time. While one Tape Transport is operating on-line, the other Tape Transport may be operated simultaneously to perform off-line functions. The Card Reader / Punch or Line Printer may, at program option, be selected to receive data from the Core Memory; or the Card Reader / Punch may be selected to transmit data to Core Mem-ory. Each Tape Transport, Card Reader / Punch, or Line Printer requires a speci-fic address for on-line operation. All address~ng and data transfers between the Magnetic Tape Console and the Central Processor are via the Uni-Record Trunkline.

Section VIII Paragraph 8.1

All off-line operations are under operator control. Off-line operations include data transfer between the Tape Transport and Card Reader / Punch, data transfer from the Tape Transport to the Line Printer, or data transfer from the Card Reader/

Punch to the Line Printer. Tape Transport to Tape Transportopel"ation is not pos-sible. Off-line data transfer is not possible between Magnetic Tape Con$oles.

8. 1 TAPE TRANSPORTS.

Each L-3555 Magnetic Tape Console contains two Tape Transports as well as the control sections for a Card Reader/Punch and Line Printer. L-3556 Magnetic Tape Consoles do not contain control sections for a Card Reader / Punch or Line Printer.

On each Tape Transport, data is recorded at a density of 556 characters to the inch, operating at the rate of 90 inches per second. Records are separated by 3/4 inch inter- record gaps.

The end of file indication is a 3 inch gap followed by an end of file character. The 3/4 inch inter-record gap follows the end of file character. Tape can be read and recorded with either odd or even parity. Maximum tape start plus stop time is 7 milliseconds; minimum is 5 milliseconds.

Some degree of simultaneous operation is provided, in that, a data transfer tion can be in process on one Tape Transport, overlapping non-data transfer opera-tions bn other Tape Transports; i. e., Rewind, Backspace Record, Backspace File, Skip Record, Skip File, Write File Mark.

Tape may be moved forward or backward; however, operations requiring data trans-fer can take place only while tape is moving forward. Forward is from left to right, over a split head. This split head has a write station and a read station. During recording the read station checks the parity of each character 3 milliseconds after it has been recorded.

After the tape start time of 3. 5 milliseconds has passed, data is transferred at the rate of 50,000 characters per second. Maximum tape stop time is 3. 5 milliseconds also.

Tape normally moves at the rate of 90 inches per second. There are two rewind speeds: a hi-speed 270 inches per second, and a low-speed of 90 inches per second, paragraph 8. 1. 4.

8. 1. 1 TAPE "TRANSPORT ON-LINE READ.

Section VIII Paragraphs 8. 1. 1 to 8. 1. 1. 3

For program testing of the On-Line, Off-Line status of a Tape Transport, refer to Section VII.

On-line Read operation is accomplished in one of two ways: Normal Input and Con-trolled Input. In both cases, the data is read into Core Memory starting with the location specified by the effective operand address of the Input instruction.

8. 1. 1. 1 DATA FLOW. Data is read from tape a character at a time into the Mag-netic Tape Console Control Section. Then the data is transmitted to the Uni-Record Interface in the Central Processor. Having collected a full word, the Interface

transmits that word through the M register into Core Memory. The Operand portion of the Interface Instruction register, and/ or the Interface Word Counter are modi-fied immediately after each word is stored in Core Memory.

8. 1. 1. 2 END OF TRANSFER. Data transfer can be terminated by any of the follow-ing conditions: end of operation, end of file, error. These conditions and their programming implications are discussed in the description of the Normal and Con-trolled Input instructions in paragraph 8. 1. 1. 4.

If transfer is terminated short of a complete record, the tape continues to move until an inter- record gap is reached. The unread portion of the record is passed over and the Interface is notified by an Incomplete Record signal.

Where the Controlled Input instruction is used, and the number of words specified by the Word Counter is greater than the number of words in the record, the tape will move over the inter- record gap and read words from the next record. If the

specified word count is greater than the number of words available when a file mark is read, the Interface is notified by an Overload signal.

8. 1. 1. 3 ERROR CHECKING. Vertical parity is checked as the tape is read into the Tape Console Control Section. At the end of each record, the horizontal check char-acter is checked. Parity is checked again at the M register.

If a parity error is detected during data transfer, the last correct word is stored.

An incorrect word is not stored unless either the Uni-Record Interface Error Inter-rupt toggle is ignored, or the error is an M Register Parity Error, specifically the least significant character. In either case, the Tape Transport will continue mov-ing tape until the next inter-record gap is reached.

Section VIII

Paragraph 8. 1. 1. 4

8.1. 1. 4 TAPE READ OPERATION.

Command Character I

Instruction IZYXMMMM

Options Index, Indirect Address, Tagged Halt, Flag Return

Mnemonics RDT, RDTXR

a. Controlled Input (Y6

=

1) - Read N Words - RDTXR. An Input instruction ad-dressing a Tape Transport will cause data to be read into the Core Memory. The data words transferred will be stored in consecutive memory locations, beginning with the location specified by the effective operand addres s of the Input instruction.

The number of words to be transferred is specified by the Uni-Record Interface Word Counter which must be preloaded, paragraph 7.3. When the Word Counter has been decremented to ~~~, one more word is transferred, and the operation te rm ina te d.

The Interface remains busy throughout the operation. When the operation is termi-nated, the Interface requests an Interface Not Busy Interrupt.

The Interface is notified via an Incomplete Record signal if the number of words specified doe s not complete a record. Although data transfer is terminated, the tape will continue to move until an inter- record gap is reached.

When a file mark is sensed an End of File signal is sent to the Interface, the word,

i'/J'/J'/J'/J'/J'/J'/J,

is transferred to the Central Processor, and the operation is terminated.

However, if the Word Counter has not been counted to '/J'/J~ when end of file is sensed, an Overload signal is transmitted.

When an end of tape marker is sensed, an End of Tape signal is sent to the Interface;

however, the operation continues~

Should the tape have a record which ends in a partial word (from another system), the partial word will be padded with zeros.

When an error occurs, the Word Counter can be used to implement error recovery.

The Word Counter content will have been decremented by the number of words transferred.

b. Normal Input (Y6 :::

'/J) -

Read One Record - RDT. An Input instruction with theY6 bit OFF will cause data to be read into the Central Processor. The data words transferred will be stored in consecutive Core Memory locations, beginning

Section VIII Paragraphs 8. 1. 2 to 8. 1. 2. 3 with the location specified by the effective operand address. Reading and data trans-fer will continue until an inter-record gap has been sensed. When all of the data has been transferred, the Interface requests an Interface Not Busy Interrupt, to com-plete the operation. The Interface remains Busy throughout the operation.

When a file mark is sensed, an end of file indication is sent to the Interface, the word,

-V/J'/J'/J'/Jr/J(/J'/J,

is transferred into Core Memory, and the operation is terminated.

When an end of tape marker is sensed, an End of Tape signal is sent to the Interface, however, the operation continues.

The Uni-Record Instruction register in the Central Processor is of significant value in error recovery since it will reflect the point of termination.

Im Dokument General Precision, (Seite 156-162)