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Functions that were incorporated in the previous Toshiba original microcontrollers.

  • #1 Large current port


    We are starting a new series to introduce functions which were incorporated in the previous Toshiba original microcontrollers. Do you miss DTF, DTMF, OSD and VCR servo? The function we will introduce “large current port” as the first topic.

    A short while ago, display units of home appliances were mainly light-emitting diode (LED). For applications that a number of seven-segment LED are used, such as clocks, method called “dynamic lighting system” was used, and which switches digits by lighting a digit for tens of milliseconds. A lot of you have seen that images of home appliances in TV pictures were flickering.
    Brightness of previous LEDs was not high. To achieve bright display in dynamic lighting system, 20 mA of current per segment (one pixel) was required, and which was required to the specification of microcontrollers as well. Toshiba’s original microcontrollers, such as TLCS-47 series and TLCS-870 series, had about eight pins that can carry up to 30 mA for each pin. LED display was achieved by connecting the cathode side of LED and delivering large current to the LED. This large current port was used to drive relays in addition to LED.
    The use of seven-segment LED small-size displays in recent home-appliances is decreasing and high-luminance, low-power LEDs have been commercialized. So, large current ports are no longer contained in microcontrollers.
    LEDs being used as illuminations are increasing, however, those being used as displays are decreasing. Because, now Eco-friendly (power-saving feature) and graphical user interface are required more than ever.
    The memory of early microcontrollers with eight red LEDs makes us feel the flow of era…

  • #2 VFT driver


    Although the fluorescent display was generally called Vacuum Fluorescent Display (VFD), the circuit built in the Toshiba microcontrollers was called the Vacuum Fluorescent Tube (VFT) driver. The VFD was bright in bluish white and was often used for the time display with VCR. However, since it is difficult to display colors in dots and there is much consumption current, other displays have been replaced by it.
    As you know, the VFD is a kind of a vacuum tube, it needs to add around -40 V (minus voltage!?) for turning on the light. The ports of microcontrollers had the P channel source open drain structure to withstanding the voltage, and had around 50 ports for grid (digit selection) and segment. The display system was a dynamic lighting system which repeats turning on a part momentarily. The dimmer function which changes a display and brightness automatically was built in microcontrollers as a display control circuit. Since it was clearly reflected also in a dark room, the VFD was luxury those days.

  • #3 DTMF generator and receiver

    Cell phones and smart phones use digital communication but fixed telephones use analog circuits. The way to transmit a telephone number with an analog circuit in a traditional way was connect and disconnect in a short period. For example, a set of disconnection and dis-connection was performed to transmit “1”. “9” was 9 sets of connection and disconnection and “10” was 10 sets. It takes so much time to dial in this method, and data communication was difficult after connection, because lines were disconnected.
    This is where Dual-Tome Multi-Frequency (DTMF) comes in. The sound of the DTMF was made by relating the 4-type sounds (697, 770, 852 and 941Hz) of lower band to the other 4-type sounds (1209, 1336, 1477 and 1633Hz) of upper band 16 keys, and allocating them to 16 keys, such as numbers from 0 to 9 and symbols like # and *. They were as known as a push button signal and a tone signal.
    There were dialer specific ICs, however most of telephones output DTMF signal using microcontrollers. As for Toshiba microcontrollers, the 4-bit TCLS-47 series microcontrollers, such as TMP47C451BN, TMP47C452BN/BF and TMP47C453AN/AF, and the 8-bit TLCS-870 series microcontrollers, such as TMP87CM53F, incorporated the DTM generator. These microcontrollers used unusual oscillator which oscillation frequencies were like 480 kHz, 960 kHz and 3.84 MHz.
    Once the calling-sides use DTMF, receivers also started using DTMF, as a remote controller to listen to recorded message from a remote location. In this case, DTMF signals need to be converted to instruction codes, therefore, microcontrollers that contain a DTMF receiver were released. As for Toshiba microcontrollers, TMPM47C850N/F of the TCLS-47 series.
    As for software for telephones, dial input was recorded for a slow output dial pulse by using a ring buffer that produce infinite output (by not accepting a key if it nearly overflows). This process was controlled by an input pointer and an output pointer.
    Well, the time when I had a hard time with this processing is now fading from my memory…

  • #4 On-screen Display (OSD)

    The OSD is a function to show channels and volume on a TV monitor. In the era of analog televisions, televisions were controlled by a single microcontroller, which controls a remote control signal reception, power supply, volume and selects channels and audio video (AV). The current status was described in characters on a screen and 4-bit, 8-bit microcontrollers were used at that time. The current digital TVs look the same, but now system LIS has a controlling role and microcontrollers are no longer used.
    Regarding the OSD of analog televisions, setting display position, characters, character size and character color, the OSD circuit shows the information about those items. The OSD circuit keeps watch over vertical scanning lines and horizontal scanning lines and turns on a dot from R output (red), G output (green) and B output (blue) for 1-dot width.
    Some Toshiba microcontrollers, such as the TMP47C434N of the TLCS47 series for TV applications, the TMP87CS38N/F of the TLCS-870 series, the TMP88CS38BN/F of the TLCS870/X series and the TMP90CS74EDF of the TLCS-90 series for VTR applications, had OSD circuits. The early stages of OSD had squarish fonts only. While higher function is continuing, various functions became available, such as smoothing, slanted fonts, edging and underlined.
    Advancing capabilities of televisions, display patterns using OSD were diversified, for example, image enhancements and sound quality adjustment, and the processing is more complicated. At that time, development works were carried out while a television cover was removed. I remember I was afraid to go near television sets that high voltage was applied.

  • #5 Closed Captioning Decoder

    We introduce functions which were incorporated in the previous Toshiba original microcontrollers. The fifth issue is a closed captioning decoder.
    Closed captioning decoders are the system created in the United States for displaying subtitles for deaf and hard of hearing people.
    The Television Decoder Circuitry Act requires television receivers with picture screens 13 inches or larger to have built-in decoder circuitry designed to display captions. This requirement had to be carried out by January 2004, so the function to support transfer of caption data was also mounted on Microcontrollers for TV. In this system, received caption data is displayed on a TV screen by using the on-screen display which was introduced in the previous issue.
    It was incorporated in Toshiba microcontrollers as a “data slicer”: TMPA8700CSF of the TLCS-870 series with OSD function for TV application and TMP88CS38NG of the TLCS-870/X series. The data slice indicates that a circuitry device data into slices to receive, because caption data of the analog broadcasting was superposed on a vertical fly-back period. The screen is displayed by scanning from top to down. The vertical fly-back period is a period that a signal to be scanned returns from bottom to top. There is no video information in this period, so a caption text data was superposed.
    This caption text data was useful not useful for deaf and hard of hearing people, but foreigners who are learning English as well.

  • #6 Melody/alarm generator

    A melody/alarm generator is contained in the Toshiba microcontrollers for electric pocket book and electric dictionary, such as the TMP92C815F of the TLCS-900/L1 series. These microcontrollers controlled electric pockets by integrating other parts, such as a LCD controller, a real-time clock and an external memory controller.
    The melody function can easily outputs square wave from 4 Hz to 5461 Hz and makes melody by outputting the waveform for arbitrary interval. For example, writing 023H to the setting register output a sound that represent the “la” tones of the scale.
    The alarm generator can output the sound of 4096 Hz in eight patterns. Beep sounds can easily made and which are used for different purpose such as a key clicking sound and an error sound.


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