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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING CD-ROM based CD player. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment Recently, CD-ROM drives have become an indispensable attribute of a modern computer. However, recently, due to the rapid increase in the speed of information exchange and the cheapening of high-speed models, more and more "old and leisurely" goes on their last journey - on the shelf, swallow the dust (and in the worst case - for spare parts). Now the price for 2 - 4-speed models ranges from 40-75 hryvnia (models with control buttons are somewhat more expensive). And although the sound quality provided by CD-ROM drives is much worse than in stationary CD players, it is still higher in comparison with cassette recorders. The main obstacle to the use of CD-ROM drives as standalone CD players is the lack of any disc playback controls. And although there are models with control keys, they, unfortunately, do not provide any service functions. There are two options for solving this problem: you can find reference data on the control processor of the drive - perhaps it allows you to connect control keys, or you can control the drive the way a computer does it - through the drive interface. I must immediately make a reservation: the first option is a practically hopeless business, while the second, although fraught with additional material and time costs, is a win-win. To date, there are several schemes of this kind. Two of them were published in the Radio Amateur magazine, another one was advertised in one of the echo conferences of the FIDO network. Unfortunately, all these schemes have their drawbacks, namely: the need for control keys on the front panel of the drive, the lack of firmware for the microcontroller and the non-IDE interface (Radio Amateur No. 1/98) and, again, the lack of firmware for the third circuit, which, Naturally, it makes it difficult to repeat them.Considering all of the above, it was decided to develop an inexpensive CD-ROM drive controller, to some extent free from these shortcomings. So briefly about what kind of device it is and what it is for. This circuit is a controller for controlling a CD-ROM drive with an IDE interface and is designed to implement the ability to play music CDs. In addition, the controller can be used to check the drive's performance (this firmware version does not support this feature). The Z80 (DD3) processor was used as the control processor. There are two reasons for this choice: firstly, when developing something, you most often have to be content with what is at hand, and, secondly, this processor, as well as devices based on it (Caller ID and ZX-Spectrum, which gather dust half-disassembled on the shelves many), is quite widespread. For example, I used the old AON board, since most of the connections there are already wired.
On the elements DD1.1-DD1.3 of the DD1 (K1533LN1) microcircuit, a master crystal oscillator is assembled, from the output of which a clock sequence with a frequency of 4 MHz is fed to the clock input (leg 6) of the processor. On the elements DD1.4-DD1.6, an interrupt pulse generator is made. The short pulses of negative polarity taken from its output with a frequency of about 400 Hz are fed to the input of a maskable interrupt (leg 16) of the processor. The volume of RAM and ROM (chips DD7 (K573RU10) and DD5 (2764)) is 2KB and 8KB, respectively (the maximum volume is 32KB and 32KB), which makes it possible to use almost any memory chips. The device memory map looks like this: Address Memory type 0000H-1FFFH ROM 2000H-27FFH RAM. 2800H-FFFFH Reserved for RAM and ROM expansion. On the DD2 chip (K1533ID7), an address decoder for external devices is made. To reduce the number of microcircuit packages, and, consequently, to reduce the cost of the device, a dynamic display method was chosen. The character image is latched into the DD8 K1533IR23 register (the address for the 7FH entry corresponds to it), and the code corresponding to the number of the highlighted bit is latched into the DD9 K1533TM9 register (the address for the 3FH entry). The digit number code is decrypted by the DD4 K555ID10 microcircuit. A keyboard port is made on the DD6 K1533KP11 chip. Keyboard port address - 3ЕH (read). The keyboard is a matrix of 4x4 normally open buttons. The keyboard columns are connected to the inputs of the keyboard port, and the rows are connected to the outputs of the scan decoder (DD4). The number of buttons can be easily increased to 36, for this it is enough to solder the keyboard matrix by analogy with the existing one, using the remaining outputs of the DD4 decoder, with the exception of the output R9 (leg 11) which is involved in the formation of the reset signal for the CDROM drive. To match the eight-bit data bus of the microprocessor with the sixteen-bit data bus of the CD-ROM drive, a node includes three microcircuits: DD10 (K1533AP6) and DD11-DD12 (K1533IR23). Bus shaper DD10 provides decoupling of the microprocessor data bus and the lower half of the drive data bus, and registers DD11-DD12 - fixing the data coming to the upper half of the drive data bus when reading or writing. The lower half corresponds to the base read/write address F0H, and the higher half corresponds to BFH. (Note: since the CD-ROM drive has 8 registers through which data is exchanged and controlled, then, accordingly, it, as an external device, corresponds to 8 addresses for input and output, in this case - F0H-F7H). Thus, to write data to a CD-ROM, you must first write the high byte to address BFH, and then write the low byte to the required address from the F0H-F7H range. To read data, you must first read the low byte (address - F0H-F7H), and then read the high byte from the port with the address BFH. Theoretically, a properly assembled device does not need to be adjusted. However, in practice, it may be necessary to adjust the frequency value of the interrupt pulse generator - it should be 400 Hz Chips of the K1533 series are replaced by their counterparts from the K555 series. The Z80 processor can be replaced by the Soviet counterpart K1858VM1. The multiplexer K1533KP11 (DD6) can be replaced by a bus driver K1533AP5, K1533AP6 or even four elements of the K555LP8 chip. Instead of the DD8 register K1533IR23, the K1533IR27 register can be installed, while pin 1 of the microcircuit must be connected to log.1 or to pin 26 (reset circuit) of the processor. Instead of register DD9 K1533TM9, you can use either K1533IR27 (pin 1 is connected similarly to the previous version), or K1533IR23. The given controller ROM firmware does not provide any service functions. In fact, its main purpose is to show that the controller circuit is operational. This in no way means that new firmware versions will not appear. Perhaps they will appear by the lnlemrs of the article's release. So, this firmware provides the following functions: 1. Playback of audio discs with indication of the current track number and playing time (key "2"); 2. Go to the previous track (key "1"); 3. Transition to the next track (key "4"); 4.Stop playback ("3" key); 5.Pause/resume playback ("6" key) 6.Disc ejection ("7" key). The inserted disc is automatically recognized and ejected if it does not contain any audio tracks. The given firmware has been successfully tested on the following models of CD-ROM drives:
Author: Roman Ivashchenko; Publication: N. Bolshakov, rf.atnn.ru
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