--- In , "hc08jb8" <hc08jb8@y...> wrote: Hi Jay, See http://www.ezl.com/~rsch/projects.htm#SPI for hardware & software. Roger > Hi All, > > I have seen some schematics where a HD44780 based LCD is hooked up > using 74HC164 or 74HC595 (serial shifter chips, I guess), this mode > only uses a few pin resource on the MCU. I did look at the datasheets > of the 164/595 but couldnt figure out much on the software part. > > 1.) How does the MCU talk to these chips and effectively control the > LCD? > 2.) Is it using SPI protocol? > 3.) If I need to initialise the LCD and start sending strings to > display, where should I start? > > Thanks in advance > Jay

Jay -- See below --- Avoid computer viruses, Practice safe hex --- -- Specializing in small, cost effective embedded control systems -- http://www.smithmachineworks.com/embedprod.html Robert L. (Bob) Smith Smith Machine Works, Inc. 9900 Lumlay Road Richmond, VA 23236 804/745-1065 ----- Original Message ----- From: "hc08jb8" <> To: <> Sent: Thursday, January 08, 2004 12:30 PM Subject: [68HC12] HCS12 LCD with 74HC164 or 74HC595 > Hi All, > > I have seen some schematics where a HD44780 based LCD is hooked up > using 74HC164 The 164 is a simple, serial-in / parallel-out, shift register. It does not have latched outputs or an asynchronous output register clear. > or 74HC595 (serial shifter chips, I guess), The 595 is also a serial-in / parallel-out shif register. It does have latched output registers, but does not have an asynchronous output register clear. The preferred device for your application is the 594 which replaces the Output Enable function of the 595 with an asynchronous reset that clears the output latches. > this mode > only uses a few pin resource on the MCU. I did look at the datasheets > of the 164/595 but couldnt figure out much on the software part. You can easily drive the 594 more or less directly with the SPI port. The general idea is that you shift in an eight bit word and then strobe it into the output registers using the latch clock. You change the data on the output bus each SPI sequence to step the 44780 LCD driver through its required sequence of commands and data transfers. > > 1.) How does the MCU talk to these chips and effectively control the > LCD? By sending command words to the 44780 via the SPI port, using the 594 as a registered latch to emulate a bus sequence. > 2.) Is it using SPI protocol? Yes. > 3.) If I need to initialise the LCD and start sending strings to > display, where should I start? Start at the beginning of the initialization command sequence. As I recall the first command declares your intent to operate in 4 or 8 bit transfer mode. You use the 4 bit mode by connecting 4 of the output data bits of the 594 to matching data bits of the 44780. You also connect other output bits of the 594 to the register select pin and the R/W pins of the 44780. Finally, you have to connect the enable pin of the 44780. You can use one of the 594 pins, but it is best if you can spare a direct output port pin of the HC12 to run the enable. This saves you from having to grind through 2 complete SPI cycles to toggle the data into the 44780. Finally, in a similar manner, if you can afford 2 or 3 output pins on the HC12 you can directly connect and bit bang the RS and Enable pins. Since you can drive the 44780 in the Write Only mode, the R/W pin can be hard wired. This all enables you to run the 44780 in the 8-bit mode which saves many, many SPI cycles. If my memory serves me well, there was an example of running LCDs off of the SPI interface at http://www.eio.com Best wishes, Bob Smith > > Thanks in advance > Jay > --------------------To learn more about Motorola Microcontrollers, please visit > http://www.motorola.com/mcu > o learn more about Motorola Microcontrollers, please visit > http://www.motorola.com/mcu >

These are serial shift registers, indeed, and they would work with the SPI port on the '12. Suspect it would be easier to use the 595 because of its internal buffer structure that makes it more suitable for SPI. You would hook up MOSI to the SHIFT CLOCK input of the 74HC595, SCLK to the SHIFT CLOCK input of the shift register, and SS# (or any convenient port pin, set up as an output) to the LATCH CLOCK input of the shift register. The minimal hardware version would be to run the LCD in 4-bit mode, so the shift register would output the 4 data bits, plus the three control signals typically needed by the LCD-R/W#, A0 (register select), and E. The data sheets for the LCD panel (which basically echo the HD44780 data sheet) show you the signal sequence needed to drive the LCD. The software required is not theoretically difficult but a little laborious because you're effectively emulating an old 6800 parallel bus interface, using the SPI bus, one bus state at a time. Each 8-bit SPI bus transfer must set the three control signals appropriately, and the four data bits. You could also run the LCD in 8-bit mode, but then you would need to cascade two 74HC595's in series, so that you can build the three control signals. Hope this is helpful. Best regards, Kerry Berland Silicon Engines 2101 Oxford Road 847-803-6860 Fax 847-803-6870 Des Plaines, IL 60018 USA -----Original Message----- From: hc08jb8 [mailto:] Sent: Thursday, January 08, 2004 11:30 AM To: Subject: [68HC12] HCS12 LCD with 74HC164 or 74HC595 Hi All, I have seen some schematics where a HD44780 based LCD is hooked up using 74HC164 or 74HC595 (serial shifter chips, I guess), this mode only uses a few pin resource on the MCU. I did look at the datasheets of the 164/595 but couldnt figure out much on the software part. 1.) How does the MCU talk to these chips and effectively control the LCD? 2.) Is it using SPI protocol? 3.) If I need to initialise the LCD and start sending strings to display, where should I start? Thanks in advance Jay --------------------To learn more about Motorola Microcontrollers, please visit http://www.motorola.com/mcu o learn more about Motorola Microcontrollers, please visit http://www.motorola.com/mcu _____ > Service.

Hi All, I have seen some schematics where a HD44780 based LCD is hooked up using 74HC164 or 74HC595 (serial shifter chips, I guess), this mode only uses a few pin resource on the MCU. I did look at the datasheets of the 164/595 but couldnt figure out much on the software part. 1.) How does the MCU talk to these chips and effectively control the LCD? 2.) Is it using SPI protocol? 3.) If I need to initialise the LCD and start sending strings to display, where should I start? Thanks in advance Jay