The control part of the system is comprised of a principal control loop and three subroutines. The control loop is a polling process which checks the DMflags, T-clock, and R-clock, for an indication that data is to be transmitted or received. On transmission, the data in the DMflag (T-data) is transferred to the DMflag (T-out), the data in the transmit buffer, T, is shifted left one bit, and the most significant bit (shifted to OVERFLOW) is placed in T-data prior to the next clock signal. On receiving input, each new bit is shifted into the receive buffer, R. When the start bit is shifted out of R into OVERFLOW, the nine bits of the message have been received. Thus, when OVERFLOW is set, the 5-bit channel number is transferred to the analog multiplexor switch which selects the appropriate channel, and an analog sample, is taken. The T(analog-to-digital) converts the analog sample to digital form and the data is transferred to the transmit buffer, T.
TELETROLA, A MUSICAL TERMINAL
Design by Michael Knudsen
KEYWORDS: Tone synthesis, frequency division, Teletype
Most of us are familiar with devices known as electronic music synthesizers. These usually consist of various analog tone generators driven by a human playing a keyboard. In this problem we shall deal with the design of a synthesizer which generates tones digitally, and is driven by incoming, serial digital data of the form used by a Teletype.
Design a musical instrument which connects to a bit-serial communications line and interprets incoming characters as notes to be played. For the purposes of this problem, assume the bit serial line comes from a Teletype, hence the name Teletrola for the musical instrument. Since nearly all computers have interfaces for low-speed (10, 15 or 30 characters/sec) typewriter-like terminals and use bit-serial (or Teletype) format data, Teletrola could be easily interfaced with a computer.
The design should adhere to the following restrictions:
1. The terminal is a 10, 15 or 30 char/sec Teletype using the 6-bit subset of the 7-bit ASCII code of book Table 5. The data which gets transmitted to the device has only the 64-character subset, octal 040 through 137, plus carriage-return (015) and line-feed (012). This includes capital letters, special characters, and digits, but no small letters or other control codes.
2. No buffer memory is available to store incoming data. Characters must be processed (played) as received.
3. No addressable read-only memory (ROM) is available for table-lookup operations, just a few constants registers. Try for one M(constants; 4- words).
4. An adjustable Kclock is used to set a DMflag, to provide a real time measure.