Exabyte EXB-8205 Instruções de Operação descarregar pdf (Página 369)

In contrast, suppose you attempt to change the Density Code to

14h after completing step 3. The EXB-8505 returns Check

Condition status with the sense key set to Illegal Request (5h),

indicating that you can’t change the Density Code when the tape

is not at LBOT. (This is because you can only have one data

density on a tape.) Again, this result is what you would expect

and it does not depend on the EEPROM option.

Differences between the WRITE and READ Options

The differences between the WRITE and READ options become

apparent when the default writing format does not match the tape’s

actual format. These differences are illustrated in the following

example:

Example 2 Suppose you normally write and read 8500 format

tapes (Density Code 15h) with an EXB-8505, but you occasionally

need to read tapes that are written in an unknown format. To do

this, you might follow these steps:

1. Load the unknown-format tape in the EXB-8505.

2. Without issuing a MODE SELECT command at LBOT, issue

a READ command to read some data. (Because you do not

issue a MODE SELECT, the default writing format remains

15h).

3. Issue a MODE SENSE command to determine the tape’s

density. Assume for this example that the EXB-8505 returns

14h for the Density Code, indicating that the tape’s actual

format is 8200 format.

If you have the WRITE option and you now issue a MODE

SELECT command with the Density Code set to 14h (that is, you

echo back the MODE SENSE data), the EXB-8505 returns Check

Condition status. The error occurs because the EXB-8505 thinks

you are attempting to change the writing format when the tape is

not at LBOT.

If, however, you have the READ option and you issue a MODE

SELECT command with the Density Code set to 14h, the EXB-8505

completes the command and does not return Check Condition

status. However, it does not change the tape’s current format or

the default writing format. This is because the EXB-8505 interprets

the Density Code differently with the READ option than with the

WRITE option and knows that you are specifying the current

tape’s actual format.

May 1994 EXB-8205 and EXB-8505

(Standard and XL)

A-33

Appendix A EEPROM Options

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