IBM 31x Backspace 08 BS, Horizontal tab 09 HT, Line feed 0A LF, Normal Display Control Mode DC1

11-9-2005 Input/output device commands

carriage return, or display position command is written to the top line. The test and reset commands stop the scrolling message regardless of the display position.

Backspace (08) <BS>

08

Purpose:

Decrements the cursor position by one and clears any character displayed in that position. If the write position is at the lower left, the position is moved to the upper right, and if it is at the upper left, it is moved to the lower right. This commands stops the scrolling alphanumeric message if the cursor position is on the top line when this command is sent.

Horizontal tab (09) <HT>

09

Purpose:

Increments the cursor position by one. No characters are erased. This command stops the scrolling message if the cursor position is on the top line when the command is sent. At the end of a line, the display behavior is determined by the state of the display control mode as follows:

Normal Display Control Mode (DC1)

If the cursor is at the upper right position, it is moved to the lower left position. If the cursor is at the lower right position, it is moved to the upper left position.

Vertical Scroll Display Control Mode (DC2)

If the cursor is at the upper right position, it is moved to the lower left position. If the cursor is at the lower right position, the characters displayed on the bottom line are moved to the top line, the bottom line is cleared, and the cursor is moved to the lower left position.

Line feed (0A) <LF>

0A

Purpose:

The display behavior is determined by the state of the display control mode as follows:

Normal Display Control Mode (DC1)

The cursor is moved to the same position in the complementary line. In this mode, a line-feed command stops the scrolling alphanumeric message if the cursor is on the top line when this command is sent.

Vertical Scroll Display Control Mode (DC2)

If the cursor is on the top line, it is moved to the complementary position on the bottom line. If the cursor position is on the bottom line, all characters on that line are moved to the top line, the bottom

Appendix A. Input/output device commands A-5