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Basic Information
Question 1
How many startup methods are there for the 32768Hz oscillator on the HT49RA0/HT49CA0?
Answer
If using the 32768Hz oscillator with the HT49RA0/HT49CA0 there are two methods of startup, a quick startup and slow startup. Bit 4 in the RTCC register will determine which startup method is selected.
When bit 4 of the RTCC register is 0, the 32768Hz oscillator will have the quick startup function.
When bit 4 of the RTCC register is 1, the 32768Hz oscillator will have the slow startup function.
Question 2
How many interrupts are in the HT49RA0/HT49CA0 and how are they generated?
Answer
The HT49RA0/HT49CA0 provides 2 external interrupts, one internal timer interrupt, one internal time base interrupt and one internal real time clock interrupt. The interrupt entry points in the Program Memory are located at 004H, 008H, 00CH, 010H and 014H.
The external interrupts are generated by the occurrence of a transition on pins INT0 and INT1. The active transition can be either a low to high transition, a high or low transition or both types of transition, the actual type used is determined by a configuration option.
An internal timer interrupt request is generated when the timer overflows.
A time base interrupt request is generated when a regular time base signal occurs.
A real time clock interrupt request is generated when a regular real time clock signal occurs.
Functional Description
Question 1
How is the LCD frequency setup on the HT49RA0?
Answer
The LCD frequency is setup via the following:
- 1. In the configuration option setup, use the fs clock source to selected the LCD clock source. The LCD clock source can come from either the RTCOSC, WDTOSC or T1.
- 2. Use the configuration options to select an LCD frequency of 4KHz.
Question 2
What is the difference between the two bias types in the HT49RA0LCD, 1/2 bias and 1/3 bias?
Answer
In the HT49RA0LCD there are two kinds of bias, 1/2 bias and 1/3 bias. If the 1/3 bias is selected, then the highest voltage on the LCD SEGMENT and COM outputs is 3/2 VLCD. If the 1/2 bias is selected, then the highest voltage on the LCD SEGMENT and COM outputs is VLCD.
Application Description
Question 1
What are the differences in hardware circuitry for different bias types (1/2 bias or 1/3 bias) in the HT49RA0/HT49CA0?
Answer
If the 1/2 bias type is selected, then a capacitor should be connected between pin V2 and ground. Nothing should be connected to pin V1.
If the 1/3 bias is selected, then a capacitor between V1 and ground and a capacitor between V2 and ground is required. An additional capacitor is required between pins C1 and C2. All capacitor values are 0.1uf.
Question 2
How is the IR Carrier generated in the HT49RA0?
Answer
First the configuration options must setup pin PC0 as a carrier output after which the carrier frequency and duty must be selected. When the software then sets PCC.0 = 0 and PC0 = 1, then the carrier will be generated. If PC0 = 0, then the carrier output will be switched off.
Question 3
How is the timer used to measure a pulse width?
Answer
First setup the TE bit in the timer control register TMRC to determine the method of activating the timer. Then set the TON bit to 1 to enable the timer. For the situation where the TE bit has been cleared and TON is equal to 1, if the external timer pin receives a low going edge, then the timer will start counting. If TE and TON are both equal to 1 then the timer will start counting when the external timer pin receives a high going edge. When the external timer pin receives an edge having the opposite transition type from the original edge then it will stop and the TON bit will be automatically cleared. The measured value will be stored in the timer register, TMR.
Question 4
In the different timer modes, how does the TON bit change state?
Answer
The timers have three different modes, external event counting mode, timer mode and pulse width measuring mode. In the three modes the TON bit is set manually using instructions. After being enabled the timer will be activated and start counting. In the pulse width measurement mode, the TON bit will be automatically cleared after a pulse has been received. In the other two modes the TON bit can only be reset by instructions.
Question 5
In the HT49RA0, as ort PA has no PAC control register, how is the input/output function controlled?
Answer
When PA is to be used as an input, before reading the data, the related pin to be read must be set “1”. By executing the instruction “SET PA.i(i =0~7)” the related NMOS output is disabled, after which the data on the pin can be read using the “MOV A, PA” instruction.
Question 6
What method can be used to receive remote control codes?
Answer
The methods used to receive remote control codes are many. One way is to use an I/O pin or the INT interrupt pin. The difference between these two is that using the I/O pin method will consume more microcontroller run time resources as the I/O pin must be continually polled to check for a level change in order to not miss a valid signal. One way to reduce software overheads and increase efficiency is to use the timer to setup a suitable time. When the timer interrupt occurs the I.O pin can be polled. Using the INT pin however reduced resources significantly reducing the need for immediate pin sensing. However using the INT pin to receive a signal will instigate a signal process operation on a high going or low going edge and not be able to distinguish similar periodic waveforms with different duty cycles. Therefore as only the logic high or low will trigger the interrupt, software or the timer can be used to decode the signal.
Question 7
For the RTC in the HT49RA0/HT49CA0 why is it not recommended to use RTCC divider 28 ~ 211 ?
Answer
If the 32768Hz RTC oscillator is chosen as the system clock, then after a wake-up for fixed RTC interrupts, if the 28、29和210 RTC option is selected, then care must be taken. For these division ratios, as a wake-up needs 1024（210）internal clock cycles, follow on RTC interrupts may be lost.
Question 8
What is the difference between the R-type and C-type LCD bias in the HT49RA0/HT49CA0?
Answer
The R-type bias requires less components, however the C-type uses less power. If the product is a power sensitive application then the C-type bias should be selected, however it should be noted that in the C-type LCD 1/3 bias, the LCD voltage will be 3/2 VLCD.
Points to Note
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