Using the HT48R008 to Control a Bidirectional LED Array and Touch Keys

Transcription

1 Using the HT48R008 to Control a Bidirectional LED Array and Touch Keys D/N: AN0397E Introduction The HT48R008 is an 8-bit high performance enhanced RISC architecture MCU which has the advantages of low cost, low power consumption, timer functions, power down and wake-up functions as well as a watchdog timer. These low cost features enhance the versatility of the device making it suitable for a huge range of home appliances and consumer products. Operating Principles The HT48R008 internal LED driver does not require external current limiting resistors and other external components, which makes the device suitable for small home appliances panel products. The special features of the HT48R008 can be seen in its industrual quality specification (-40 C~85 C), operating voltage range of 2.3V~5.5V, OTP Program Memory capacity of 4K words, SRAM Data Memory capacity of 96 bytes, internal I 2 C and UART interfaces, internal high accuracy RC oscillator, power down and fast wake-up functions, etc. 1 / 5 AN0397E

2 HT48R008 I/O Controlling LED Array Description Hardware Figure 1 Use the HT48R008 PB, PC and PA ports as the scanning pins for the LED array (8 4 2=64) and touch keys (8 2=16), maximising the I/O functions. Timing Figure 2 One forward scan corresponds to four COMs. Each COM contains the same number of LEDs. All LEDs are switched on with the same brightness. 2 / 5 AN0397E

3 Regiser Setup Symbol I OH1 I OH2 Parameter I/O Source Current (PB, PC3~PC0) I/O Source Current (PA, PC5~PC4, PD, except PA7) Test Conditions V DD Conditions Min. Typ. Max. Unit 3V V OH=0.9V DD, PXPS[n+1:n] = ma 5V 00B, n=0, 2, ma 3V V OH=0.9V DD, PXPS[n+1:n] = -1-2 ma 5V 01B, n=0, 2, ma 3V V OH=0.9V DD, PXPS[n+1:n] = ma 5V 10B, n=0, 2, ma 3V V OH=0.9V DD, PXPS[n+1:n] = -4-8 ma 5V 11B, n=0, 2, ma 3V -4-8 ma V OH=0.9V DD 5V ma I OL1 I/O Sink Current (PA, PB, PC, PD, except PA7) 3V 8 16 ma V OL=0.1V DD 5V ma I OL2 PA7 Sink Current 5V V OL=0.1V DD 2 3 ma The HT48R008 has an internal LED driver, PB and PC ports, whose I/O sink current can be up to 32mA at 5V. The I/O source current supports a four-level output which have a current drive of up to 16mA at 5V. By using the I/O sink and source current, the LED array can be directly driven without using additional limiting resistors and other components. The I/O ports can be setup as input or output to allow driving one more LED arrays. The touch keys are scanned during the intervals between the LED COM scans. PXPS Register Bit Name PXPS5 PXPS4 PXPS3 PXPS2 PXPS1 PXPS0 R/W R/W R/W R/W R/W R/W R/W POR Bit 7~6 Unimplemented, read as 0 Bit 5~4 Bit 3~2 Bit 1~0 PXPS5~PXPS4: PC3~PC0 source current selection 00: Level 0 (min.) 01: Level 1 10: Level 2 11: Level 3 (max.) PXPS3~PXPS2: PB7~PB4 source current selection 00: level 0 (min.) 01: level 1 10: level 2 11: level 3 (max.) PXPS1~PXPS0: PB3~PB0 source current selection 00: level 0 (min.) 01: level 1 10: level 2 11: level 3 (max.) The PXPS register is used to setup the I/O source current level. 3 / 5 AN0397E

4 Program Flowchart START Initnal (init_io,init_ram,init_timer) Main 1ms_loop (key_scan, LED_display) 5ms_loop (LED_word_lib) When the program starts, first execute an initialisation including I/O ports setup, RAM setup and timer setup, then enter the main loop. 4 / 5 AN0397E

5 The initialisation includes the I/O port setup, RAM setup and timer setup, which are described below. 1. As for the I/O port setup, it is important to confirm the power on status of the I/O ports. This application uses the PA, PB and PC ports. The PA port is setup as an input push-high, the PB port is setup as output high and the PC port is setup as input. 2. The most important purpose of the RAM setup is to confirm the RAM initial status. This application clears the contents of the RAM address 040H~096H to 00H and sets the RAM to be used for the preset status. 3. The 1ms_loop program uses a time-shared multi-task architecture. Within the 1ms loop two subroutines will be executed, key_scan and LED_display. Within the 5ms loop one subroutine will be executed, LED_word_lib. The key_scan and LED_display subroutine codes are provided in the example code section. Example Description The LED_display and key_scan timings are described in figure 3. This application uses 8 SEG pins and 4 COM pins to control 32 LEDs and properly configures the I/O as input or output to implement the 64-LED array control funciton. 1 4 LEDs count as one unit multiplied by 16 groups to form an array with 64 LEDs. These are scanned at a frequency of 62.5Hz (1/16ms). The waveworm in the following figure shows the time when key_scan subroutine is executed. Figure 3 Example Code Refer to the enclosed file. 5 / 5 AN0397E