Talking to TED:
The MOS 7360/8360 Text Display ICs

by Levente Harsfalvi (TLC@MSZI.PMMF.HU)


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.


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.

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:

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 graphics 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 retrieves 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 shown, 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.

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.

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.

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 that the TED handles the keyboard matrix. A simple 8-bit input 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.


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 can be reached at the Internet address listed above or at:

Levente Harsfalvi
7200 Dombovar
Gorkij 33.

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

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
              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.
              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.
              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.

Document Revision B