
THEORY OF OPERATATION
4.13
[13] MULTI ENCODER
The majority of the circuitry for this function is provided by U17, a programmable logic device
(pld) which is programmed by U11. U11 is under control of U12 which can be set up by U17 to
provide different ROM addresses which contain the U17 programs corresponding to different
encoder functions.
U17 includes storage and counters for the time which is gotten off the processor bus. It also
includes dividers and multiplexers to facilitate the generation of different codes and carrier rates.
U17 incorporates a counter which is clocked at one hundred times the output carrier rate.
Outputs from the counter drive an internal look-up table whose outputs drive the DAC U6. The
reference for the DAC incorporates the DC shift code, so the DAC output is a modulated
envelope. This current is converted to a voltage by U7, then buffered and output by U8.
4.14
[14] MULTI ENCODER (PLL)
The one hundred times clock comes from a counter chain driven by the output of U9, a pll
which is locked to either the generated 100KHz or the translator ZAD/. U10 is used to select
appropriate parts for the loop filter in accordance with the selected frequency and dividers. INH,
SEL0, and SEL1 are written by U24 through U17 to U12.
4.15
DISTRIBUTION BOARD (100008)
The TymMachine contains one 100008 Distribution Board Assembly. Option Plug-in
Assemblies are installed into the Distribution Board Assembly. This assembly has provisions for
installing up to four single wide Option Plug-in modules.
4.16
DISPLAY ASSEMBLY (100009)
The display uses an 8 digit driver (U1) to drive displays DS1-DS8. Data is input over line
VCOM, PB0-PB3, with address input on VCOM, PB4-PB6. Line PB7 has decimal point
information. W/ is used to store the information. The output of this driver is multiplexed constant
current segment, decimal point, and digit drive for 8 LED digits. The ninth digit of the display
(US) is driven by U2 a decoder/driver with storage, and U4 which, in combination with U3,
drives the top and bottom segments for sixes and nines, respectively. The data presented on
VCOM, PB0-PB3, is stored by LDUS/. Resistors R1-R7 limit current to match the intensity of
DS9 to the rest of the display.
This assembly also includes the keypad which is implemented with 16 switches in a four by four
matrix, and the LCD.
Symmetricom, Inc.
TM7000 TymMachine TCG/T (Rev D)
4-15