Telecommunication IC
 
   
 
Q1 :  Why could /CD be low in RA register without FSK signal?
Q2 :  What will it happen while overusing the STACK?
Q3 :  What stuff is included in the 2.8K RAM of EM78811?
Q4 :  Does PLLC pin has to be pulled to ground or to VDD in EM78 series MCU?
Q5 :  What's the relationship between RDET1 pin and RING TIME pin?
Q6 :  How do you use the instruction PAGE in EM78 series MCU?
Q7 :  How many I/Os in the 32 I/Os of EM78811 are shared pins (dual function)?
Q8 :  What's the purpose of the instruction FJMP and FCALL?
Q9 :  Questions about using RAM.
Q10 :  How will it be happened when IO port is set to output and internal PLL HIGH?
Q11 :  Why does FSK output has COOKED DATA and RAW DATA?
Q12 :  After presetting a value to COUNTER1 and CUNTER2, whether it will count from presetting value at the second time or not when up-counting is overflow?
Q13 :  Is there any cause of current consumption to be concerned?
Q14 :  What’s the relationship between POVD and LPD?
Q15 :  How do you handle unused LCD SEGMENTs?
Q16 :  What's the relationship between the instruction ADD, SUB with C flag?


  Answer
Q1 :   Why could /CD be low in RA register without FSK signal?
  A: /CD LOW means FSK signal coming in. In the other word, if signal on the TIP and RING has MARK or SPACE frequency and energy is strong enough, /CD will be low. Even if noise is coming in, it also could leads to /CD LOW. Generally speaking, this situation could be happened when ringing begins and ringing stops. You can solve this problem by doing some preamble delay checking.


Q2 :   What will it happen while overusing the STACK?
  A: If Interrupt or call subrountine is over stack layers, the first layer stack record will be canceled. Because of that, program cannot go back to the first Interrupt or instruction "CALL" point and program is easy to be confused.


Q3 :   What stuff is included in the 2.8K RAM of EM78811?
  A: There is 2.5K CLID RAM controlled by RC、RD in the 2.8k RAM. LCD RAM has 120 BYTE controlled by IOCB、IOCC. Others are 144 BYTE general memory. Total memory is 2.764K BYTE。


Q4 :   Does PLLC pin has to be pulled to ground or to VDD in EM78 series MCU?
  A: PLLC is the part of Phase Locked Loop and it could be grounded with bypassing capacitor or connected to the power. If it is grounded in low frequency mode (GREEN MODE), PLLC is ground. If it works in high frequency mode (NORMAL MODE), PLLC pin will has about 1.2~2 V voltage. We can test the voltage on this pin to judge whether MCU works in high frequency mode or in low frequency mode. When PLLC is connected to the power, PLLC has power level in low frequency mode (GREEN MODE). Otherwise; it has 2V voltage drop in high frequency mode (NORMAL MODE).


Q5 :   What's the relationship between RDET1 pin and RING TIME pin?
  A: When ringing is coming in, RDET1 level will change to high level. At the same time, a transistor in the internal RINGTIME is turned on and discharging. This will lead to RINGTIME pin to low level. RINGTIME internally series with a BUFFER to RA register’s /RD. If you don’t want to use these functions, pull RINGTIME to VDD and RDET1 to ground.


Q6 :   How do you use the instruction PAGE in EM78 series MCU?
  A: Use “PAGE @” in your program to change the value of R5. For example, use “PAGE @1” then the value of R5 is 1.


Q7 :   How many I/Os in the 32 I/Os of EM78811 are shared pins (dual function)?
  A: I/O has PORT6、PORT7、PORT8、PORT9. PORT6 are shared with COMMON8 to COMMON15. PORT8 are shared with SEGMENT44 to SEGMENT51. PORT9 are shared with SEGMENT52 to SEGMENT59.


Q8 :   What's the purpose of the instruction FJMP and FCALL?
  A: Now our IC doesn't have the instruction FJMP and FCALL but Compiler. Itself supports these two macro instruction. Because PAGE only needs to check whether PAGE of destination and PAGE of R5 are the same before these two instruction JMP and CALL, we eagerly suggest that you have better control PAGE by your own. It is easy to do. However, while using the instruction FJMP and FCALL, COMPLIER will insert some lines of instructions to enlarge your program. And it will lead to the problem of program manager.


Q9 :   Questions about using RAM.
  A: No need to take care of PAGE problem from 0x10 to 0x1F in EM78 series MCU . Because of that, the user can distribute these RAM to important parameters such as data backup of interrupt, and so on. However, the user should take more care of 4 PAGEs for 0x10 ~ 0x3F. Whenever the different PAGE is used, it must reset register RSR(R4) bit6 and bit7.


Q10 :   How will it be happened when IO port is set to output and internal PLL HIGH?
  A: This is a big BUG. Because PLL HIGH resister is about 300k, it will lead to about 17uA(5V/300k) current consumption when output level is low. If you have 8 low level outputs, the current consumption will be 136uA. So it is good way to use PULL HIGH in input.


Q11 :   Why does FSK output has COOKED DATA and RAW DATA?
  A: The format of FSK includes pre-leading signal Preamble which is 150ms '0'-'1' interlacing signal (CHANNEL SEIZURE) and 100ms '1' signal (MARK). After MARK, it is intelligent FSK data signal (FSK DATA). So called RAW DATA means such format of FSK. That is to say RAW DATA is Preamble and FSK DATA. And COOKED DATA is FSK DATA only without Preamble. Due to different test environment in the different country, we suggest using RAW DATA to handle FSK data. With that, software control is more flexible to face different test environment.


Q12 :   After presetting a value to COUNTER1 and CUNTER2, whether it will count from presetting value at the second time or not when up-counting is overflow?
  A: If the MCU donot have auto-reload function. It begins to count from zero so we hope it always has a preset value. You have to reset the countering value after each interrupt. Because it could be a little of error form interrupt to writing-in preset value, there will be some error for the time of interrupt. So we can’t make a precise count. It can’t get a precise time of interrupt unless we let it free count without writing-in preset value.


Q13 :   Is there any cause of current consumption to be concerned?
  A: The 8-bit CPUs series give user a large freedom. Software can control hardware in many ways.


Q14 :   What’s the relationship between POVD and LPD?
  A: Basically, POVD and LPD belong to voltage detection devices. POVD detects voltage from 1.6V to 1.8V. LPD detects voltage from 3.6V to 3.8V. When POVD detects the voltage below 1.6V, the IC is reset. But when LPD detect the voltage below 3.6V, it will only send a low voltage signal. By the way, LPD can be turned off by software but POVD can’t and it can be controlled by CODE OPTION.


Q15 :   How do you handle unused LCD SEGMENTs?
  A: Basically unused LCD SEGMENTs can be opened without connection and nothing to do with them because they are output pins.


Q16 :   What's the relationship between the instruction ADD, SUB with C flag?
  "A:The usage of the addition ADD instruction ---- When the value of ACC adds to a number or the value of register and the result is over 255, the flag C will be set to 1. Oppositely, if the result is less than 255, the flag C will be set to 0. The usage of the subtraction SUB instruction ---- As a mater of fact, SUB instruction does the same thing with ADD instruction. The difference is taking 2’complement plus 1 of the subtraction value as the addition value. That is to say A – B = A + (2’complement of B + 1). So if A + (2’complement of B + 1) is over 255, the flag C is set to 1. Oppositely, the flag C is set to 0. For example : 0xAA – 0x11 = 0xAA + 0xEF ? Over 255, then C = 1 0xAA – 0xBB = 0xAA + 0x45 ? Less than 255, then C = 0"