Pin Functions Of Intel 8279 Interface - Watkins-Johnson Company WJ-8718A/MFP Instruction Supplement

WJ-8718A/MFP
TABLE 3-3
Refer to Table 3-1 and note that Y3 goes low when C
=
0, B
=
1, and A
=
1. These
conditions exist when AD3 (C)
=
0, AD2 (B)
=
1, and AD1 (A)
=
1 or, from Table 3-2, when the
hexadecimal address is 1046. Y3 provides the enabling pulse to the address 1046 write-only
devi'ce, U20, described in paragraph 3.1.3.14.
3.1.3.3 Intel 8279 Programmable Keyboard/Display Interface (Ul, U2)
The 8279 interface chip is designed for use with the Intel 808SA Microprocessor,
located in the IF Interface (MFP-A3). The microprocessor is programmed to command the
operating characteristics of the interface chip, enabling the interface to provide LED indicator
and display drivers with information derived from front panel scans or data stream from a
remote control device (if an optional remote interface is used). The interface automatically
scans the front panel keyboard and refreshes the display, relieving the microprocessor of these
tasks. .
Table 3-3 lists the functions of the input and output lines of the 8279 interface
which are used in this MFP application. FigUre 3-3 is a block diagram of the interface chip
showing key functional areas which are discussed in paragraphs 3.1.3.3.1 through 3.1.3.3.4. The
functional and operational characteristics of the Group 1 interface (U1) and its associated
external decode/driver circuits are discussed in paragraphs 3.1.3.3 through 3.1.3.8; the Group 2
interface (U2) and its associated external circuits are discussed in paragraphs 3.1.3.3 and 3.1.3.9
through 3.1.3.1.3.
Table 3:"'3. Pin Functions of Intel 8279 Interface
Designation
DBO - DB7
CLK
RESET
AO
SLO - SL3
RLO - RL7
OUT BO - B3
Function
Bidirectional data bus lines which transfer data between
the interface and the microprocessor bus.
Clock from external RC network which is used to
generate internal timing.
Raised high by the microprocessor to reset the internal
circuits of the interface.
A low level enables the receive or transmit functions of
the interface.
Defines the functions of DBO - DB7 signals: AO low,
data; AO high, command/status.
A low level enables data to be transmitted to the micro-
processor bus via DBO -DB7.
A low level enables data to be received from the micro-
processor bus via DBO -DB7.
Used to scan switch matrix columns.
Return lines from switch matrix rows; lines connect to
scan lines through closed switches.
Output lines synchronized to scan lines to provide data to
the external display segment/indicator LED anode drivers.
Blanks the display during digit switching or by command.
3-9