REWIND INSTRUCTIONS

Two rewind FS's are provided, rewind-with-inter-lock and rewind-without-interrewind-with-inter-lock. Either rewind can be executed through the read or the write channel of the synchronizer.

The channel through which a rewind-without-inter-lock FS is accessed remains busy while initiating the operation for at least 182 but not more than 367 microseconds. After the operation has been initiated, the channel is free to accept the next FS. Thus, one unit can rewind while other units read and write.

However, if a rewind-with-interlock FS is specified, the synchronizer remains busy for about 11 milli-seconds. If a rewind FS is accessed on one channel while the other channel is idle, both channels of the synchronizer remain busy for the times mentioned above.

Rewind Without Interlock

The rewind-without-interlock FS causes tape from the takeup reel to be passed to the supply reel until the load point is reached; at this point the rewind is complete, and the UNISERVO tape unit may be ad-dressed. If a UNISERVO tape unit is addressed during a rewind, the busy indicator (table 3-2) is set, and

UNISERVO tape units may be rewound simultaneously, but the rewind FS's must be supplied separately.

SUPPLY REEL (QUICK-CHANGE HUB)

TAPE CLAMP

VACUUM COLUMN

READ &

WRITE HEADS

PHOTOCELLS:

LOAD POINT AND END-OF-TAPE

WARNING

TAPE SYSTEM Operating Characteristics

TAKE-UP ---\.----REEL

~-+ ________________ ~ __ ~ __ ERASE HEAD

Figure 3-2. Tape Path

VACUUM COLUMN

TAPE SYSTEM

Function Specifications

UNISERVO IliA COMPATIBLE MODE

In addition to the usual UNIVAC III mode, individual bits in the 27-bit word can be arranged so that tapes used with UNISERVO IlIA units can also be used with the UNIVAC 490 Real Time System and the UNIVAC

1107 Thin-Film Memory Computer. This additional bit configuration is handled automatically by the

UNISERVO IlIA synchronizer circuitry.

A switch is installed on each tape unit in the UNIVAC

III System which is used to process UNISERVO IlIA compatible-mode tapes. This switch has two posi-tions, one for the usual UNIVAC III mode and one for the compatible mode. Memory bit positions for writing and reading compatible-mode tapes are illustrated in figure 3-3.

The compatible mode has 18 data bits and the

UNIVAC III mode has 25. When writing

compatible-WRITING UNISERVO lilA COMPA1"IBLE-MODE TAPES Modulo-3

Parity Parity and

127 Bits 261-25--o--B-its--t91-18---o-a-ta-B-it-s---tl Modulo-3 Parity Bits ... Not transferred to tape Parity and O-Bits ... Bits 19 through 25 are not

transferred totape. Synchronizer inserts UNISERVO IlIA com-patible-mode parity bits and O-bits on tape.

Data Bits ... Bit positions 1 through 18 are transferred to tape.

READING UNISERVO IliA COMPATIBLE-MODE TAPES Modulo-3

Parity Parity and

I

Bits 1 _ _ _ O-_B_its _ _ I _ _ _ _ _ oa_ta_B_it_s _ _ _ _ _ 1

27 26 25 19 18 1

Modulo-3 Parity Bits ... Automatically inserted in mem-ory by the synchronizer Parity and O-Bits,

Data Bits ... Bits 1 through 25 are trans-ferred to memory as they appear on tape.

Figure 3-3. Word Formats in Memory for Writing and Reading UNISERVO lilA

Compatible-Mode Tapes

mode tapes, only memory bit positions 1 through 18 are transferred to tape. The synchronizer writes either O's or compatible-mode parity bits onto tape in the bit positions that correspond to memory positions 19 through 27. When tape is read, bits 1 through 25 are transferred to memory as they appear on tape, and the required UNIVAC III parity bits are inserted automatically in positions 26 and 27.

Compatible-mode blocks must be written from con-secutive memory locations using block-read in-structions;, tape movement must be stopped between blocks.

The following list is a summary of UNISERVO IlIA ta pe-uni t specifications:

PROGRAM-CONTROLLED FUNCTIONS:

Gather-write, Block- or scatter-read,

Rewind with or without interlock, Tape-error recovery, and Load-point test.

Alphanumeric characters-133,OOO per second Decimal digits-200,OOO per second BLOCK LENGTH:

Variable-under program control INTERBLOCK GAP:

Approximately 0.6 inch TAPE CHARACTERISTICS:

Base-MYLAR Coati ng---oxide Width-Yz inch

Length-3600 feet (3500 feet recordable) Thickness-l mil

DIRECTION:

Read-forward or backward Write-forward

CHECKING:

I nformation written onto tape is checked by a read head after being written;

I nformation read from or written onto tape is modul0-3 checked;

Bad spots on tape are marked with special bit configurations which are not transferred to memory; and

Load point and end-of-tape warning are detected photoelectrically.

• FUNCTION SPECIFICATIONS

To perform a programmed tape operation, the

UNISERVO IlIA tape-unit synchronizer requires an initiate-input-output-function (IOF) instruction and a function specification (FS). The IOF instruction

identifies the UNISERVO IlIA input-output channel to be used and specifies the address of the FS.

Details of the tape operation are specified in the FS, which has the following format:

Function

12512:'P' u

n~1120

Tape Unit ... Binary representation of tape unit to be used

Function Code ... Specifies operation to be performed on designated tape unit

I ... Controls interrupt-if it is a I-bit, a program interrupt occurs when execu-tion of the FS is completed; otherwise, this interrupt will not occur.

L-Address ... For block-reads, used as base address (in binary); for gather-writes and scatter-reads, represents location of first SCAT control word.

The individual function codes with their mnemonics are described under the headings which follow.