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PD243X Fiches technique(PDF) 3 Page - OSRAM GmbH |
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PD243X Fiches technique(HTML) 3 Page - OSRAM GmbH |
3 / 7 page 2000 Infineon Technologies Corp. • Optoelectronics Division • San Jose, CA Appnote 49 www.infineon.com/opto • 1-888-Infineon (1-888-463-4636) OSRAM Opto Semiconductors GmbH & Co. OHG • Regensburg, Germany www.osram-os.com • +49-941-202-7178 3 May 31, 2000-14 Figure 3. PD2435 block diagram showing the major blocks and internal registers Application The speed regulated moving message display is an example where a digitized value of the controlling analog signal is used to compute a reload value for the Timer 2. The Timer 2 is oper- ated in mode 0 where this reload value becomes a starting point for the Timer to count up. On overflow the Timer automat- ically takes the restart value for counting from reload register CRC. While the Timer is counting up, a new reload value is computed using the present A/D value. Hardware The circuit used in this application has the advantage of requir- ing a minimum of components. The single chip microcomputer SAB 80535 operates in conjunction with four alphanumeric programmable display chips PD 2435 to form a 16-digit long display. The ASCll-coded data is transferred from the SAB 80535 to the display ICs via the data port P0 and using the control signal WR (P3.6) of the SAB 80535. The address pins from the ports P0 and P2 of the SAB 80535 are used to address the EPROM as well as the display chips in a memory-mapped l/O scheme. The display chips are addressed as memory locations with the fol- lowing addresses. Display Chip Control Register Address Digits Address 1 1000H 1004H-1007H 2 2000H 2004H-2007H 3 4000H 4004H-4007H 4 8000H 8004H-8007H DISPLAY MEMORY (RAM) 4 x 8 CTL REG 1 x 8 DECODE & MIX CE0, CE1 A0 – A2 RD, WR CLK SEL XCK RST OSC LOGIC DISPLAY MULTI- PLEXER COLUMN DRIVERS OUTPUT LATCH ROW DRIVERS OUTPUT CONTROL LOGIC 3 D0 – D7 8 14 1 1 3 7 3 4 5 8 15 128 CHAR. ROM 48 x 80 DISPLAY 20 20 7 A push button is interfaced to port P3.2 of the SAB 80535 to provide an external interrupt to the microcontroller. Firmware Description Besides controlling speed of the moving message, there is a provision to interrupt the moving message and roll it backwards to the beginning of the message. The microcontroller reads the code and the message to display from an EPROM 2716A inter- faced to the ports P0 and P2 of the SAB 80535. A virtual image of the message is created in the internal RAM of the SAB 80535. Four display chips PD2435 are interfaced to the SAB 80535 in a memory-mapped scheme and can be addressed as external memory to the SAB 80535. The virtual image of the message in internal RAM of the SAB 80535 is used to manipu- late data to be displayed on the display chips. The internal RAM used for the display can be viewed as an area divided into two portions: 1. For active display 2. As a data buffer The active display area is the replica of the data being displayed on the display chips. In this case the 16-digit display would need 16 RAM locations which correspond to 16 digits currently being displayed. The data buffer contains the rest of the message which is not being displayed. The message is shifted character by character in the RAM area. When the message on the dis- play moves from right to left, the RAM buffer acts in “First In First Out” mode, and when the message on the display moves from left to right, the data to the display from the microcontrol- ler RAM buffer is supplied in the “Last In First Out” scheme. Between display of every character there is a software delay which depends upon the level of the analog signal supplied to the ANO pin of the SAB 80535. The external interrupt 0 (at port P3.2) is used to interrupt the microcontroller to inform it that the message needs to be scrolled backwards. On getting this interrupt the software sets the flag bit 0 which remains set until the message is scrolled back to the beginning of the message. List of Components Reference Material for ICs 1. SAB 80515/80535 User’s Manual. 2. PD2435 Data-Sheet or Optoelectronic Data Book (1990). Name Number SAB 80535 1 271 6A 1 PD2435 4 12 MHz Crystal 1 74LS373 1 22 pF Capacitors 2 100 nF Capacitor 1 4.7 µf Capacitor 1 1 k Resistor 1 10 k Pot 1 |
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