COMMAND LINES DECODES - FUNCTIONAL COMMANDS DESCRIPTION The function of the five command lines (CMDO-4) has been

previously described (Table 5-6). A detailed description of the decoded functional commands follows.

5.4.1 Read Forward Command (00000)

The Read Forward command causes tape to be moved in the forward direction to read a block of data. Non-data characters are detected, decoded, checked for validity, and used for their specific purposes, but are not transferred across the interface.

Data is transferred until End Of Data is detected. The Last Word (FLWD) line is ignored if issued during a read operation.

5.4.2 Read Reverse Command (0 1 000)

The Read Reverse command causes tape to be moved in the reverse direction to read a block of data. Non-data characters are detected, decoded, checked for Validity, and used for their specific purposes, but are not transferred across the interface.

Data is transferred until End Of Data ;s detected. The Last Word (FLWD) line is ignored if issued during a read operation.

When the 50 IPS Read Reverse operation is completed the read head is positipned in the Inter Block Gap (IBG) preceding the data block.

When the· 100 IPS, streaming mode, Read Reverse operation is completed, positioning of the read head in the IBG is not guaranteed.

5.4.3 Write Command (00100)

The Write conmand causes tape to be moved in the forward direction and the following to take place;

1. The ending portion of the preceding IBG is written,

2. The data block is written and simultaneously read and checked for validity, .

3. The beginning portion of the next IBG is generated

Non-data characters of the data block are automatically generated, encOded, formatted and written. Data characters to be written arrive from the interface, are automatically encoded, formatted, and·written.

The overall write conmand execution sequence is as follows;

1- User asserts the .Write conmand and the FGO 1; ne,

2. MTSacknow.ledges· FGO by asserting Formatter Busy (FFBY),

3. MTSacknowledges Write by asserting Data Busy (FDBY) and starts motion,

· 4 .. MTS asserts Data Write Strobe (FDWDS) pulses until user asserts Last Word (FLWD); the host does not respond - data is assumed to be correct and on time,

. ^{. .}

5. MTS continues to move tape to perform read back check. When data transmission and status accumulation are completed, the MTS drops . FDBY to enable user to read the status and issue

the next conmand,

6. If the user does not issue a new conmand, the drive stops and FFBY is dropped.

5.4.4 Write File Mark Command (00110)

This command causes tape to move forward and a tape mark block to be written and checked for validity. Two retries are automatically done.

5.4.5 Write Extended Command (01110)

This command allows the host to change the Inter Block Gap (lBG) length for streaming mode operations (100 IPS). The command requires a one byte write transfer to completely define the operation. Formatter Busy (FFBY) and Data Busy (FDBY) remain asserted throughout the transfer. The byte sent defines the gap size selection as follows;

00 hex

=

nominal lBG

01 hex

=

nominal IBG + 0,3 in. (0.76 cm) 02 hex = nominal IBG + 0.6 in. (1.52 cm)

When a gap length has been selected by the Write Extended command, Long Gap (FLGAP) is ignored until the gap has been set back to nominal by another Write Extended command.

5.4.6 Fixed Erase Command (00111)

This command causes tape to move forward and the following lengths of tape to be erased;

PE = 3.6 in. (9.14 cm) nominal GCR = 3.4 in. ( 8 . 64 cm) nom; na 1

During the erase operation, read checks are performed to verify that erasure took place. If read signals are detected, Data Check is asserted in Status Byte O.

5.4.7 Controlled Erase Command (00101)

This command causes the MTS to move and erase tape continuously unti 1 the Last Word signal from the user is asserted. This

terminates the erase operation.

When the erase command is given from BOT, an ID Burst is written before erasing starts.

5.4.8 Data Security Erase Command (10 111 )

This command causes the MTS to erase tape from its present position to a position approximately ten feet (3.05 meters) past

the End Of Tape (EDT) marker.

When the erase command is given from BOT, an ID Burst ;s written before erasing starts,

5.4.9 Space Forward Command (00001)

This command causes tape to move forward and pass over one block of data. If no new command is given while Formatter Busy (FFBY)

is still asserted Data Busy (FDBY) is false, the read head is positioned in the IBG following the data block. No data characters are checked for validity or transferred across the

interface.

5.4,10 Space Reverse Command (0 100 1)

This command causes tape to move backward and pass over one block of data. If no new command is given while Formatter Busy (FFBY)

1sst111 asserted Data Busy (FDBY) is false, the read head is positioned in the IBG preceding the data block. No data characters are checked for validity or transferred across the

interface,

5.4.11 File Search Forward Command (Ignore Data) (000 11 )

This command causes tape to move forward, passing over each data block encountered until a Tape Mark block is detected. Tape motion is halted with the read head positioned in the IBG . following the· tape mark, No data characters are checked for

validity or transferred across the interface.

5.4.12 File Search Reverse Command (Ignore Data) (0 1

a

¹¹⁾

This command causes tape to move backward, passing over each data block encountered until a Tape Mark block is detected. Tape motion is halted with the read head positioned in the IBG preceding the tape mark. No data characters are checked for validity or transferred across the interface.

5.4.13 Select PE Command (10011) information accumulated in the MTS registers. Eight sense bytes are issued. See next heading for sense bytes descriptions.

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