Hardware manual

EUROCOM-17-5xx 3 Programmers Reference
Hardware Manual 61
3.4.3 Address
Generator
The address generator has five write-only registers. The three transfer
address registers TRLSB, TRMIB, and TRMSB determine the address of
the first displayed pixel of each frame. When the transfer increment
register TRINC is programmed to a value larger than the line length and
synchronous transfer mode is selected in the graphics mode register
GRMODE, the address transfer register can be used to implement
horizontal and vertical paning. When the SPLIT bit in the GRMODE
register is set packed line mode is selected, which allows a resolution of
up to 1152 x 900 with 8-bit per pixel. The ENOVERL bit enables 8-bit per
pixel plus 4-bit overlay mode. PIXDEL is used to adjust horizontal
backporch of the digital output with one pixel resolution. This is necessary
for exact positioning on flat panel displays.
3.4.4 LM1882 Sync
Generator
The EUROCOM-17-5xx implementation of the LM1882 uses Auto
Addressing Mode and Auto-Load Mode (/LBYTE tied to high). For
proper operation the bits B0 to B2 of REG0 must be programmed to either
%100 or %110. Cursor location of the LM1882 is used to initiate the
address transfer cycle for the next frame. Therefore cursor location must
be programmed to be active for one line after the last displayed line. The
cursor signal may be routed to LIRQ4 input of the VIC to trigger
interrupts synchronous to the video signal.
3.4.5 Pixel Model The video memory consists of two VRAMs (4-Mbit chips) with a total
size of 1MB and provides the serializer with an 8-bit x 4 data stream. The
parallel port of the video RAM is 32-bit wide. Each byte represents one
pixel in 8-bit mode allowing a resolution of 256 colors. The first displayed
pixel of a longword is located at the lowest byte address. The last is
located in the highest byte address of this longword. The first displayed
longword of a frame is located at $0FC0.0000 plus the address stored in
the transfer address registers TRLSB, TRMIB, and TRMSB of the address
generator (top of screen address). Addressing a video line has to be done
by adding a multiple of the address increment (pitch) to the top of screen
address.