6 register usage, 1 breshenham’s algorithm line draw, 6 register usage -13 – Cirrus Logic EP93xx User Manual

Page 277: 1 breshenham’s algorithm line draw -13, Table 8-20

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DS785UM1

8-13

Graphics Accelerator

EP93xx User’s Guide

Note:The word count for this example would be: 6 - 1 = 5 words, since P6 ends in the 6th word.

The word count takes into account the whole pixel, not just the starting location. So,
WIDTH = 0x5 would be written to the

“BLKDESTWIDTH”

8.6 Register Usage

Since some registers have different meanings based on the type of transfer being performed,
the next section will give the use and meaning of the register during the various graphics
transfers.

8.6.1 Breshenham’s Algorithm Line Draw

The following sequence describes how to set up the registers that are used for a
Breshenham algorithm line draw:

1. Setup LINEINIT Register

Write YINIT = 0x800 (2048) and XINIT = 0x800 in the

“LINEINIT”

2. Setup LINEPATTERN Register

A. Write desired values to the Pattern (PTRN) and Count (CNT) fields to create solid or

patterned lines. The

“LINEPATTRN”

value and a 16-bit Pattern (PTRN) that defines 16 pixel on/off patterns for line
functions. CNT specifies the position of the last bit used in the PTRN field starting at
bit 0 of the PTRN field.

B. For a solid line, write CNT = 0xF and PTRN = 0xFFFF to the

“LINEPATTRN”

“BLOCKMASK”

C. For a pattern of 8 ‘on’ pixels and 8 ‘off’ pixels, write CNT = 0xF and PTRN = 0x00FF

to the

“LINEPATTRN”

written to the MASK field in the

“BLOCKMASK”

either be transparent as specified by BG = ‘0’ in the

“BLOCKCTRL”

the color value written to the

“BACKGROUND”