Most of the information needed to support the MC44011 is contained in the Motorola application note.. It is important to follow the instructions regarding the crystal selection. The crystal must be the type that can be pulled to the colorburst frequency. The RGB inputs and the Pixel clock PLL are not used. Provisions are made to provide minimal buffering components. A 6 pin header is used to allow access to the component (Y-R/B-R) video. While not used this can be connected to a PAL delay line for non north American applications. The 68HC11E2 was selected due to the low cost and availability. Port E is not used. Port C is used as an input. 4 pairs of switches control Brightness, Contrast, Color, and Hue. Since the application note suggests that the flags be read often. Port B is connected to a row of LEDs. Port D is used to connect to the Macintosh serial port via a buffer. This leaves port A for the I2C bus. Port A was chosen over port D due to the position of the pins. The I2C is a simple clocked serial bus. Port A is configured for general I/O. Bit 5 of port A which is an output is used to generate the clock. On the E series of the hc11 Port A bit 3 can be used as either an input or an output. This pin was closer so it was used for the data bit. Bit 1 is connected to the field ID output of the 44011. The other bidirectional pin 7 is used to provide a pulse at the beginning of an I2C start condition. This is useful for debugging the bus. The driver program is encoded into EEPROM at location F800. The reset vector is pointed to this location. The micro-controller is set to run in single chip mode. If the brightness down button is closed on reset the program will jump into a monitor at location FE00. Normal operation on reset is to copy the default register settings into page 0 ram. The registers are mapped on a 1:1 basis starting at location 77. After this copy takes place. The micro-controller sends these default settings to the 44011 and wakes it up. If the Hue down button is closed during reset. The system will be set for composite video onto pin 1 of the 44011. Normal operation is for YC video, with Y on pin 1 and C on pin 3. When port C is clear the processor enters a poll loop. Interupts are not used. Port C is polled until a bit is closed, a timeout occurs, or Bit one of port A changes value. If a port C switch is closed the Page 0 value is updated and the value sent to the 44011. If a timeout occurs or the field state changes value the flags are read and displayed on port B. Then Port D is checked to see if there is a message from the host computer. These are single byte commands. All lowercase. r- reads the Page 0 registers to Port D serial out. This is a binary transfer w- sets the registers in block from Port D serial in. This is a binary transfer v- Sets a single value of a given register. The Register ID and value are Binary values. There is no validation on the writes. s- Sets the registers in the EEPROM. It copies a short communications program to location 90 in Page 0 ram. This copies the RAM Value back to the EEPROM. m- Jumps to the mini monitor at location FE00. Flag updates, or switch settings are not read in monitor mode. Construction of the video processor is not difficult. As per the Application notes standard components are used. The prototypes were built in the following order. First install the Power regulation circuitry. Provisions are made for a 5 volt regulator. Since the 44011 draws a lot of current. Use a Heat sync on the 7805. Check the board for clean power distribution. Next the micro-controller support circuitry was installed. This can be a wire wrapped unit such as the CGN-1001 available from JDR. or the support pull-ups can be placed separate on the board. This includes the Switches and the LEDs. Colored LEDs were used to represent the different flags. The switches can either be mounted on the PCB or mounted remotely in the case. The micro-contoller can then be installed and connected through a suitable buffer to the host. It should be programmed at this time. If all is working then the brightness down button can be closed. the chip should enter the monitor. Jumping to the normal reset point should cause the LEDs to flash in order. Then they should all turn on except the PLL high voltage flag which is masked inverted. Grounding pin 3 should cause the Flag LEDs to invert with only the masked bit on. When the micro-controller is working, install the Video input pull-ups and clamps. Install the output pull-ups and drivers. and the PLL filters. Check for correct voltage and signal. If all is working install the 44011 and the crystal. apply a video signal to the inputs. Connecting or disconnecting the video should cause the flags to update. If the system does not lock onto the colorburst. Check the trimmer on the Xtal. See the application note for troubleshooting info. If it working, connect the display. Using the Macintosh the registers can be set/adjusted in real time via a serial buffer into port D. These can then be written back into the rom as needed.