
ON-SCREEN DISPLAY
S3C880A/F880A
13-22
HALFTONE SIGNAL CONTROL REGISTER (HTCON)
The halftone function lets you output halftone control signals to peripherals such as a chroma-IC. You can select
halftone output for character back ground periods (as selected by bit 13 in the video RAM) or for frame periods
(regardless of the bit 13 setting). The halftone signal control register, HTCON, has the following functions:
— Halftone option selection (character or frame)
— Halftone display enable/disable
— V-sync interrupt enable and pending control
— Polarity selection of RGB and halftone outputs
Bits 4 and 5 are used for OSD Row interrupt function.
OSD ROW Interrupt Control
The S3C880A/F880A has a total of 12 OSD display rows. When enabled, an OSD ROW interrupt occurs in the
first line of each row. Up to 12 OSD ROW interrupts can be generated, while this number can be reduced
according to different settings in top margin (ROWCON.7–.3), inter row space (ROWCON.2–.0), vertical
character size (CHACON.7–.6), and Vsync blank time (VSBCON). The ROW counter of DSPCON.7–.4 informs
the order of an OSD ROW interrupt occurring within a frame. An OSD ROW interrupt is generated at the
beginning of a ROW (for ROW0 through ROW11).
OSD ROW interrupt allow different controls to each ROW. If the OSD control register is adjusted in the N-th row
area, the new value is applied from (N+1)th row. That is, if the OSD control register is adjusted in the first OSD
ROW interrupt (DSPCON.7–.4 = 0000B) service routine, the new value is applied from ROW1. A change in the
12 th OSD ROW interrupt service routine affects the rows from ROW0.
NOTE: OSD output enable/disable (DSPCON.0) settings are immediately applied. Top margin (ROWCON.7–.3) and
VSBCON are applied in accordance with Vsync input signals.
Halftone Option Selection
In character periods only (HTCON.2 = “0”), the character specified in COLBUF.3 may have the halftone function
according to the condition of DSPCON.2–.1 (DSPCON.2–.1 = "10" or DSPCON.2–.1 = "11").
In all frame periods (HTCON.2 = “1”), the entire section can have the function, regardless of the COLBUF.3
condition.