Wyse WY-60 Maintenance Manual page 85

8051 Microprocessor (U1)--The terminal has a single-component
control-oriented microprocessor which contains 256 bytes of
random-access memory (RAM), 16 input/output (I/O) lines, three
16-bit counter/timers, and a universal asynchronous receiver/
transmitter (UART). It has integral interrupt and clock
circuitry. The microcontroller uses eight data lines multiplexed
with the lower eight address lines. Address information appears
on these lines only when the address latch enable (ALE) signal is
present. The upper address lines (A8-A15) are nonmultiplexed
single-direction lines. The internal UART is used for the AUX
printer port.
Gate Array(U20)--The gate array contains the functions described
below:
Beeper Driver--The gate array contains a driver that enables
a beep. The beep frequency is HSYNC divided by 20.
Attribute data latches--The attribute data latches store
both screen and row attributes for each character to be
displayed, one at a time, for the attribute generation
circuitry. Examples of screen attributes include foreground
brightness and blink rate. Examples of row attributes
include scan line count, double high, and double wide.
Video shift register--The output of the character generator
is an 8-bit parallel code. The raster scanned CRT is a
serial device. The parallel-to-serial converter converts
the parallel output of the character generator into a serial
format the CRT can use.
Video drivers and dot stretcher--Video drivers allow output
from the parallel-to-serial converter to interface with the
CRT. In addition, the dot stretcher extends the on time of
video dots so that single vertical rows of dots appear to
have the same intensity as strings of horizontal dots. The
blanking signal disables the driver so that the video output
is inhibited during vertical and horizontal retrace.
Soft-font control--The gate array contains circuitry to
control soft-font loading and generates soft-font selection
signals.
Presettable scan line counter--The gate array enables smooth
scrolling with the presettable scan line counter.
Clock generator--The gate array generates timing signals
for the CRT controller.
Blink rate generator--The gate array generates blink rate
signals for both characters and cursor.
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