Datasheet
Propeller™ P8X32A Datasheet www.parallax.com
Copyright © Parallax Inc. Page 12 of 37 Rev 1.1 9/12/2008
The 2-bit VMode (video mode) field selects the type and
orientation of video output, if any, according to Table 8.
Table 8: The Video Mode Field
VMode Video Mode
00
Disabled, no video generated.
01
VGA mode; 8-bit parallel output on VPins 7:0
10
Composite Mode 1; broadcast on VPins 7:4, baseband
on VPins 3:0
11
Composite Mode 2; baseband on VPins 7:4, broadcast
on VPins 3:0
The CMode (color mode) field selects two or four color
mode. 0 = two-color mode; pixel data is 32 bits by 1 bit
and only colors 0 or 1 are used. 1 = four-color mode;
pixel data is 16 bits by 2 bits, and colors 0 through 3 are
used.
The Chroma1 (broadcast chroma) bit enables or disables
chroma (color) on the broadcast signal. 0 = disabled, 1 =
enabled.
The Chroma0 (baseband chroma) bit enables or disables
chroma (color) on the baseband signal. 0 = disabled, 1 =
enabled.
The AuralSub (aural sub-carrier) field selects the source
of the FM aural (audio) sub-carrier frequency to be
modulated on. The source is the PLLA of one of the
cogs, identified by AuralSub’s value. This audio must
already be modulated onto the 4.5 MHz sub-carrier by the
source PLLA.
Table 9: The AuralSub Field
AuralSub Sub-Carrier Frequency Source
000
Cog 0’s PLLA
001
Cog 1’s PLLA
010
Cog 2’s PLLA
011
Cog 3’s PLLA
100
Cog 4’s PLLA
101
Cog 5’s PLLA
110
Cog 6’s PLLA
111
Cog 7’s PLLA
The VGroup (video output pin group) field selects which
group of 8 I/O pins to output video on.
Table 10: The VGroup Field
VGroup Pin Group
000
Group 0: P7..P0
001
Group 1: P15..P8
010
Group 2: P23..P16
011
Group 3: P31..P24
100-111
<reserved for future use>
The VPins (video output pins) field is a mask applied to
the pins of VGroup that indicates which pins to output
video signals on.
Table 11: The VPins Field
VPins Effect
00001111
Drive Video on lower 4 pins only; composite
11110000
Drive Video on upper 4 pins only; composite
11111111
Drive video on all 8 pins; VGA
XXXXXXXX
Any value is valid for this field; the above
values are the most common.
4.10.2. VSCL – Video Scale Register
The Video Scale Register sets the rate at which video data
is generated, and is shown in Table 12.
Table 12: VSCL Register
VSCL Bits
31..20 19..12 11..0
PixelClocks FrameClocks
The 8-bit PixelClocks field indicates the number of clocks
per pixel; the number of clocks that should elapse before
each pixel is shifted out by the video generator module.
These clocks are the PLLA clocks, not the System Clock.
A value of 0 for this field is interpreted as 256.
The 12-bit FrameClocks field indicates the number of
clocks per frame; the number of clocks that will elapse
before each frame is shifted out by the video generator
module. These clocks are the PLLA clocks, not the
System Clock. A frame is one long of pixel data
(delivered via the WAITVID command). Since the pixel
data is either 16 bits by 2 bits, or 32 bits by 1 bit (meaning
16 pixels wide with 4 colors, or 32 pixels wide with 2
colors, respectively), the FrameClocks is typically 16 or
32 times that of the PixelClocks value. A value of 0 for
this field is interpreted as 4096.
4.10.3. WAITVID Command/Instruction
The WAITVID instruction is the delivery mechanism for
data to the cog’s Video Generator hardware. Since the
Video Generator works independently from the cog itself,
the two must synchronize each time data is needed for the
display device. The frequency at which this occurs is
dictated by the frequency of PLLA and the Video Scale
Register. The cog must have new data available before the
moment the Video Generator needs it. The cog uses
WAITVID to wait for the right time and then “hand off”
this data to the Video Generator.
Two longs of data are passed to the Video Generator by
with the syntax WAITVID Colors, Pixels.
The Colors parameter is a 32-bit value containing either
four 8-bit color values (for 4 color mode) or two 8-bit
color values in the lower 16 bits (for 2 color mode). For