Originally published in the ASCII magazine "C= Hacking" issue 12 (March 1996):
@(#)gfx: Talking to TED: The MOS 7360/8360 Text Display ICs
by Harsfalvi Levente (TLC@MSZI.PMMF.HU)
@(A): Introduction
This information file is based on my old books, descriptions, and especially
my experiences while I was coding. That's no mistake. The Plus/4 series
was not very famous in the world, but they were very poular in mideast
Europe. In fact, there were even demo groups for the machine. I learned
some of this information while writing demos for the machine in demo groups,
while other things were gleaned from personal work on the machine. These
computers did indeed play an important part in Commodore computer history.
I started my first code development on a Plus/4 in late 1986. After I saw a
HomeLab 3 (made in Hungary, U880 - GDR made Z80 compatible proc, B/W, 16K),
I started writing demos and other software for the Plus/4 machine I owned.
It actually wasn't that strange to see demo groups sprout up for all
kinds of machines, including the Plus/4. All over, there were groups
and individuals, writing software while trying to keep the flame lit for
each machine. In fact, I know people currently working in groups writing
for the Plus/4 in Hungary, Germany, and as far away as Alaska.
@(A): Overview
Let's discuss the TExt Editor (TED) IC and its environment. This DIL-48 IC
was designed specifically for the 264 series of machines, which initially
included the CV364 and the 264, evolving into the Plus/4, C16, and C116
machines. Unlike the CIA or ACIA or other machines, this IC isn't well
suited to any other system.
The TED contains all functions done by several chips in former Commodore
computers. The TED is a complete video-interface and composite video
signal generator, sound generator, keyboard input latch, timer,
clock generator, memory manager and DRAM refresher in a single IC. It can
address the full memory map of the 264 series machines, and it generates
the RAS', CAS', and MUX signals for the DRAM memory used in that series.
For ROM, it generates the chip select (CS) lines, depending on the state
of the internal registers. So, in addition to all the above duties, the
TED IC is a simplistic MMU as well.
@(A): Video Information
We see the TED chip shine as it does its primary job, displaying graphics.
Its abilities mostly parallel those of the uniquitous VIC-II video IC in the
C64. It has the following modes:
* 40x25 screen (characters)
* enhanced color mode
* multicolor mode
* 320x200 Hi-Res Graphics
* 160x200 Multicolor Graphics
Of course, there are differences. TED does not contain sprite support.
To offset this omission, the TED chip can select 8 intensities for each of
the 16 supported colors, giving 121 colors (the 8 shades of black are all
black). Other features include a hardware cursor, hardware text blinking,
and hardware inverse character support. Character sets, screen and color
memory, and graphics bitplanes can be addressed directly, without additional
logic as found on the C64. In fact, even RAM/ROM selection requires change
of a single bit.
Character modes need $800 bytes of RAM for screen and color memory. The
first $400 bytes act as color memory (the memory permanently located at
$d800 on the C64), with the lower 4 bits containing color codes, exactly
as found on the 64. Bits 4-6 denote the intensity level of the color, while
the high bit select flashing/no-flashing attributes. The other $400 bytes
contain the screen codes for the displayed characters. If hardware
character inversion is selected, the lower 7 bits hold the screen code and
the high bit selects inversion for the character. If character inversion
is not selected, all 8 bits denote the screen code. Extended Color Mode (ECM)
and Multi Color Mode (MCM) modes work exactly as described on the 64. While
these two modes are in effect, inversion and blinking are disabled.
Things get a bit more complex in graphics mode (pun unintentional). In
graphcis mode, the bitplane occupies $2000 bytes and is handled just like a
VIC-II biplane. The colors are handled differently. $800 bytes are needed
for color memory, which is laid out in $400 bytes of intensity memory
and $400 bytes of color memory. An "off" bit in the bitplane uses the
lowest nybble of the appropriate color memory location as the color and
retreieves the intensity from bits 4-6 of the appropriate intensity memory
location. For an "on" bit, the color is taken from the high nybble of the
appropriate color memory location, while the intensity is taken from bits
0-2 of the intensity memory location. Bits 3 and 7 in intensity memory are
unused.
In multicolor mode, differences abound. The 64's VIC-II enabled one to
utilize 3 different colors in each 8x8 cell and a single background. The
TED simply cannot accomplish this due to the lack of adequate color memory.
So, TED allows only 2 varying colors per 8x8 cell. Those colors are chosen
from the palette of 121. The remaining 2 colors are chosen for the
entire screen, again from the 121 color palette. The mapping is as
follows:
00 background color
01 same as "off" color in hires mode
10 same as "on" color in hires mode
11 another "background" color
The TED IC is able to generate both PAL and NTSC compatible signals from
a single IC. Only the crystal need be changed to go from one standard to
the other. In PAL mode, there are 312 lines hown, while NTSC only has 262
lines of display. The line synchronization is the same in either PAL or
NTSC mode. It's always 57 clock cycles per rasterline. The TED divides
the supplied crystal frequency by 20 for PAL display and by 16 for NTSC.
For the serious video programmer, raster interrupts are implemented as on the
VIC-II. However, the 0 line of the register corresponds to the first line
of the character screen area, not the top of the border. In addition, the
current raster line can be read from TED registers. you can modify the
counter as well. Doing so will most likely affect the screen display. As
a bonus, the horizontal location of the raster can be read and modified in
the same way. Unfortunately, these registers provide the basis for most
effects, as the TED can't handle sprites.
@(A): Running The Show
As earlier mentioned, the TED IC does more than produce graphics. One of
its tasks involves generating the clock signal for the 7501/8501
microprocessor. The clock is not constant, as it switches from from
885 kHz and twice that speed, 1.773 Mhz. The speed depends on TED's current
task. It generates the slower clock signal when refreshing DRAM or fetching
data for the video screen. Otherwise, the high clock signal is generated.
The user can disable fast clock generation via a register. The end result
is a machine that operates at approximately 1 MHz, as the CPU runs in slow
mode while the screen is displayed, and operates in fast mode when the
TED starts drawing the top and bottom borders.
@(A): Sound Advice
As far as a sound device is concerned, the TED doesn't stack up to the
SID in the 64. Just 2 squarewave generators, of which the second can be
switched to generate white-noise, are available for sound generation.
Volume control is available in 8 levels.
To play samples, the TED can switch the sound generators to constant level
outputs. D/A is then done by changing the volume register setting. Each
generator can generate frequencies from 100Hz to 23kHz.
@(A): Other features
The timers available in the TED appear to be nothing more than 16
bit decrementing timers. They are always clocked with the slow clock.
The first timer reloads its starting value when it reaches 0, the other 2
are free-running.
Since it already does almost everything else, it's not unusual to notice
the TED handles the keyboard matrix. A simple 8-bit imput latch handles
keyboard interfacing.
As noted above, a single bit in the register space will page ROM or
RAM into the upper 32kB of the address map. Since the TED knows what is
paged in at all times, it knows what to output to access the memory
locations in this area.
@(A): Conclusion
Well, that about wraps up the TED IC. All that is left is a map of the
registers. Assume all registers are read/write unless noted otherwise.
If you have questions, I cna be reached at the Internet address listed above
or at:
Harsfalvi Levente
7200 Dombovar
Gorkij 33.
Hungary
By the way, catch FLI ED. V1.0; Its info file may contain some more about
TED's screen-handling. It may be retrieved as
ftp://ftp.funet.fi/pub/cbm/plus4/tlc/cns.lzh
@(A): Register Map
Register Description
-------- -----------
$ff00- $ff01: Counter #01. It always starts to decrement from the last
written value into it.
$ff02- $ff03: Counter #02. It runs freely from $ffff.
$ff04- $ff05: Counter #03. Same as above.
$ff06 : Mostly the same as VIC's $d011.
Bit 0,1,2 : Vertical smooth-scrolling
Bit 3 : 24/25 rows screen
Bit 4 : Blank screen
Bit 5 : Bitplane mode
Bit 6 : Enhanced color mode
Bit 7 : TED's internal test, it should be 0.
$ff07 : Most similar VIC-reg is $d016.
Bit 0,1,2 : Horizontal smooth-scrolling
Bit 3 : 40/38 columns screen
Bit 4 : Multicolor mode
Bit 5 : TED stop. If set, the TED stops it's counters and
screen-generating, only single clock and refresh
cycles remain.
Bit 6 : PAL/NTSC. 0:PAL, 1:NTSC
Bit 7 : Disable reverse mode. If 0, we got 128 characters
and higmost bit tells if the character should
appear in inverse. If set, no inverse mode but
256 characters.
$ff08 : Keyboard input latch. Giving a strobe - writing to the register,
the latch stores the values of the input-lines. Then, we
can read them from this register.
$ff09 : Interrupt request register. When a counter sends want to send
an IRQ, it's bit will appear as a 0; then, if the IRQ was
caused then highmost bit is set.
Bit 0 : Unused
Bit 1 : Raster-counter
Bit 2 : Lightpen. Not implemented.
Bit 3 : Counter #1
Bit 4 : Counter #2
Bit 5 : Unused
Bit 6 : Counter #3
Bit 7 : Interrupt occured. This bit is set when an IRQ
was enabled and therefore, the IRQ was sent to the
processor. Physically, this is the negated level of
the TED's IRQ output. The IRQ should be deleted
with writing the register-value back after
accepting an interrupt.
$ff0a : Interrupt mask register. These bits could be used to disable and
enable interrupt-sources. When a place is set to 1, that will
be able to cause an interrupt to the processor. If not, the sign
of the interrupt request will only be appear in the above
register.
Bit 0 : 9th bit of $ff0b (see there)
Bit 1 : Raster-counter
Bit 2 : Lightpen. Not implemented.
Bit 3 : Counter #1
Bit 4 : Counter #2
Bit 5 : Unused
Bit 6 : Counter #3
Bit 7 : Unused
$ff0b : Raster interrupt register. Same as $d012 when writing; it stores
the position of occuring raster interrupt. Higmost bit is in
$ff0a's 0. bit.
$ff0c,$ff0d : Hardware-cursor position (10 bits). Lower bits: $ff0d, higher
2 bits in $ff0c's 0. and 1. places. Beyond 1000 the cursor is
not seeable.
$ff0e : This reg is the first sound-source's frq-value's lowmost 8 bit.
More 2 bits are in $ff10's 0. and 1. places.
$ff0f : 2nd. source, lowmost 8 bits. More 2 bits in $ff12, 0. and 1.
places.
The soundregister-value can be calculated as
reg=1024-(111860.781/frq[Hz]) (NTSC)
reg=1024-(111840.45 /frq[Hz]) (PAL)
$ff10 : 1st. sound-source, higmost 2 bits. 2-7 bits are unused.
$ff11 : Sound control register.
Bit 0-3 : Volume. Maximum value is 8.
Bit 4 : Sound #1 on/off.
Bit 5 : Sound #2 squarewave on/off.
Bit 6 : Sound #2 noise on/off. If You set both, the square
will sound.
Bit 7 : D/A mode. See above for more.
$ff12 : Bit 0,1 : 2nd sound-source, highmost bits.
Bit 2 : Character generator in ROM or RAM. When set, TED
will enable ROM when trying to get data from the
charactergenerator to build screen. Else, it will
give out control-signals to the DRAM's.
Bit 3,4,5 : These bits tell, where to find bitplane in the
memory when using bitplane-mode. TED assumes them
as A15,A14 and A13 bits. So, the bitplanes can be
switched as 8K pages, anywhere in the 64K.
Bit 6-7 : Unused.
$ff13 Bit 0 : A sign to having control about memory paging. This
bit always sets to 1 when ROM is active over $8000.
Else, it will be 0. READ ONLY.
Bit 1 : Force single clock mode. Then, TED will disable to
generate twiee clock.
Bit 2-7 : Charactergenerator. Bit 7 corresponds to A15, 6 to
A14 and so on. This value shows and sets the start
of the charactergenerator. It can be paged as $400
bytes. Use with addition of $ff12-2.bit.
$ff14 Bit 0-2 : Unused
Bit 3-7 : Start of the video-ram. Bit 7 also corresponds to
the A15 line as above. So, video-ram is mappable
as $800 bytes - 2K. The above $ff12-2.bit doesn't
affect this, but the actual RAM/ROM mapping (see at
$ff3e/$ff3f and $ff13/0) does.
$ff15 : Background. Lower bits contain color-code, higher 3 luminance
and higmost is ignored.
$ff16 : Color-reg 1
$ff17 : Color-reg 2
$ff18 : Color reg 3. This and the above are used in ECM and MCM modes.
$ff19 : Border. All color registers use codes as described in $ff15.
$ff1a : Bit 0-1 : Higmost bits of the next $ff1b
Bit 2-7 : Unused
$ff1b : Actual character-position. Higmost bits in the above register.
TED counts the characters that it had fetched and put out to
the screen. The number is increasing by 40 after every
characterline (8 rasterline).
$ff1c : Bit 0 : Higmost bit of $ff1d
Bit 1-7 : Unused
$ff1d : Actual position of vertical scanning. Higmost
bit is in $ff1c. Read/Writeable!
$ff1e : Actual position of horizontal scanning. R/W!. Lowmost bit is
unused. It contains the TED's internal counter's highmost 8
bits. So, it increases 4 with every character. When writing,
it seems to put the value to a functionally different register
(writing back a reading value in right time affects the screen).
$ff1f : Bit 0,1,2 : Actual vertical scanning-line in a character-row.
R/W!.
Bit 3-6 : Flashing counter. It's value increases with every
frame, and TED fits it's flashing feature to this
register's reaching to 15.
Bit 7 : Unused
$ff3e : Switching to ROM. A writing statement to this address will
cause to turn on the ROM between $8000-$ffff. It's an other
matter, which one; this time, only sure thing that it'll give
CS signals instead of RAS', CAS' and MUX.
See $ff13/0 and $ff14
$ff3f : Switching to RAM. The opposite of the above. |
