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11. Result

In order to prevent the PCB from becoming more complex by having two layers, wires were used along with component layout. At the testing stages this lead to difficult situation. The difficulties in mounting the setup are caused by the presence of numerous wires, which can get entangled and come loose. Once the PCB layout was finalized with all the interconnections, it was a matter of replacing the wires with straight jumpers from component layout side.

12. Problems encounted

Besides the problem mentioned previously, the following is a list of other difficulties met along the way and some of the solutions.

1). The Real Time Clock DS1287 had been used for ITDL, but I found that programming it and interfacing it to the system was a troublesome process. For this, Dallas Semiconductors suggested changing DS 1287 to their latest Real Time Clock (RTC) series and I chose DS 1742 which is easily configurable and equivalent to the operation of RAM.   

2). Synchronization problem due to two crystals operating at two frequencies for MT 8870 and Z80. Employing one crystal for the both with necessary buffering has solved this.

3). Clock setting of the system by the subscriber. This is not necessary, according to the data provided by the manufacture, the RTC was capable enough to afford an accuracy of ± 1 minute a month and 10 years of operation in the absence of power. 

 

4). During the process of downloading RAM contents to the computer, there was no suitable indication to show that whether the information was being properly transferred. Therefore, a circuit with an LED indication has been associated to ITDL.    

5). ITDL should be tested for considerable amount of time period before its commercial implementation.   

6). The condition 2. of main program, Do while true has been omitted to prevent RAM get overloaded and replaced with Do Until N=16371 (3FF3h).

7). ITDL has no such indication to show the subscriber when it reaches its memory full condition and therefore no call information would be stored afterward. This facility should be incorporated to the system before commercial implementation.    

8). The length defined for Call duration (i.e. 1 Byte) in 5. Information Storage has restricted the maximum call duration. Therefore, maximum call duration storable is 255 minutes and 59 seconds. 

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Last modified: July 13, 2002