8051 Port Assignments; Additional Functional Descriptions - Wyse WY-60 Maintenance Manual

The keyboard PCB is arranged as a matrix of up to 13 rows of
eight columns each. Each key switch connects one row to one
column when that key is pressed .. The keyscanner interface chip
has 13 opendrain row outputs and eight column inputs with active
pullups. The integrated circuit communicates with the external
processor on two lines: the command line (C""MD) and the data line
(DATA) .
ADDITIONAL FUNCTIONAL DESCRIPTIONS
The logic circuitry on the terminal PCB consists of six sections:
microcontroller, communications interface, display memory,
nonvolatile memory, keyboard interface, and video control.
Microcontroller
The 8051 is a control-oriented microcontroller that contains 256
bytes of RAM, two counter/timers, a full-duplex serial port, and
two parallel ports. The processor operates at 11 MHz. This
allows most instructions to execute in 1.1 microseconds.
The 8051 has separate addresses for program storage and RAM.
IPSEN selects program storage. The terminal uses ROM for program
storage.
The microcontroller communicates over an 8-bit data bus which has
eight lower order address bits multiplexed during bus cycles.
The lower address bits are latched into an 8-bit latch by the ALE
signal. The upper eight address bits have a dedicated output
port on the 8051.
Table 6-2 is a list of 8051 port assignments.
Table 6-2 8051 Port Assignments
Port Assignment
PO.0-PO.7 Data bus and lower byte of address bus.
P1.0 80/132 column enable. Output from the 8051 to
enable the clock rate that selects 80- or
132-column mode. 0 enables the 26.580 MHz
clock and 80-column mode. 1 enables the 39.710
MHz clock and 132-column mode.
P1.1 EEPROM serial data/address. Serial data
interchange line to and from the EEPROM. Both
address and data share this line. Addresses are
serially shifted, a bit at a time, into the
EEPROM. Data is then read back serially.
6-9