Hal Communications MCEM-8080 User manual

MCEM-BOBO
MIC OCOMPUTER
SYSTEM

HAL MCEM-8080 MICROCOMPUTER SYSTEM
TECHNICAL MANUAL
*************************************************************
WARRANTY
The HAL Communications Corp. MCEM-8080 Microcomputer System is fully
guaranteed against defects in materials and workmanship for a period
of one year. Should repair or replacement parts be required
t
notify
HAL Communications torp. promptly. Please do not return your unit to
the factory for repair or adjustment until you have received a written
return authorization.
HAL Communications assumes no responsibility for the repair or replace-
ment of parts or units which have been damaged t abused
t
improperly
installed
t
or modified and reserves the right to change the design of
this equipment without incurring obligation to incorporate such changes
into existing units. Operation of this equipment with improper power
supply voltages (as described in this manual) will invalidate the
warranty.
**************************************************************
Copyright ~ 1976 by HAL Communications Corp.t Urbana, Illinois. Printed
in the United States of America. All rights reserved. Contents of this
publication may not be reproduced in any form without th~ written permis-
sion of the copyright owner.
April, 1976 Printing

MCEM-8080 MICROCOMPUTER SYSTEM
CONTENTS:
I.
SYSTEM COMPONENTS. . . ..... .
1.1
SOSOA Microprocessor ... .
1.2 Processor Control Circuitry.
1.3 Random Access Memory ...•
1.4 Read Only Memory ..•..•
1.5 Serial Input/Output (I/O) .
1.6 Parallel Data Input/Output. .
1.7
Bus Indicators and Control ..
1.S Connectors used on the MCEM-SOSO ••
2. INSTALLATION OF THE MCEM-SOSO ..... .
2.1
Initial Installation ...... .
2.2 Connection of Serial Input/Output Devices.
2.3 Connection of Power Supplies to the MCEM.
2.4 Connection of Parallel I/O Devices ..
2.5 I/O Connector Pin Assignments .•
2.6 Universal Processor Bus Connector
3. OPERATION OF THE MCEM-SOSO
3.1 Software Monitor ..
3.2 Monitor Subroutines
4. SYSTEM ADDRESS ASSIGNMENTS .•..
4.1 Random Access Memory (RAM) ..
4.2 Read On 1y Memory (ROM). • . . .
4.3 Input/Output (I/O) Assignments.
5. OPERATING HINTS .......•.
5.1 Power-on Start Up . . . . . .
5.2 Changing the Monitor Mode
.
5.3 Manually Writing a Memory Location.
5.4 Manually Jumping to a Program Address ...•.
5.5 ~anual1y Writing to an Output Port ..
5.6 Using the Break-point Register for Debug.
5.7 Using the E and R Commands for Debugging.
6.
PROGRAM EXAMPLES .
7.
SOFTWARE MONITOR LISTINGS.
8. CIRCUIT BOARD LAYOUT AND SCHEMATIC DIAGRAMS ..
9. APPENDiCES .......•............. ~
A. PROM, EPROM, ROM Connections and Markings.
B. Input/Output Jumper Connections ..•..
C. Addition of INTREQ, RESIN, and BUS EN to the UPB .
D. S080A Assembly Language Coding Forms ..
i i
..
.
.
1-1
1-1
1-1
1-1
1-2
1-2
1-3
1-3
1-5
2-1
2-1
2-1
2-9
2-9
2-10
2-12
3-1
3-1
3-5
. 4-1
4-1
4-1
4-2
5-1
5-1
5-2
5-3
5-3
5-4
5-4
5-4
6-1
7-1
S-l
9-1
9-1
9-6
9-10
9-12

TABLES:
Table 2.1
Table 2.2
Table 2.3
Table 2.4
Table 2.5
Table 2.6
ILLUSTRATIONS:
Figure 1. I
Figure 2. I
Figure 2.2
Figure 2.3
Figure ?4
Figure 2.5
Figure 8.1
Figure 8.2
Figure 8.3
Figure 8.4
Figure 8.5
Figure A. I
Figure A.2
Figure A.3
Figure A.4
Figure B.l
Figure B.2
Figure B.3
Figure C. 1
ASCI I Character Code •.
Baudot Character Code. .
Oscillator Frequency and Period.
Power Requirements and Connections
I/O Connections .••.......
Universal Processor Bus Connections.
MCEM-8080 Microcomputer System ..
EIA -RS-232C Serial I/O (standard jumpers).
Dual current loop serial I/O ..•
Single current loop serial I/O ..
Bit assignment and timing for parallel output.
Bit assignment and timing for parallel input
MCEM-8080 circuit board layout .•
Schematic drawing conventions .•.•
MCEM-8080 CPU Interface / Control.
MCEM-8080 Processor Memory . . •
MCEM-8080 Input/Output Interface
Memory jumpers for 3624-4 PROMs.
Memory jumpers for 8704 EPROM ...•
Memory jumpers for 8708 or 8308 ROMs
PROM color coding. . ....
EIA -RS-232C Serial I/O Jumper Locations.
Dual current loop serial I/O Jumper Locations.
Single current loop serial I/O Jumper Locations.
Addition of RESIN, BUSEN, and INTREQ to UPB •.•.
iii
2-2
2-3
2-5
2-9
2-10
2-12
iv
2-6
2-7
2-8
2-11
2-11
8-2
8-3
8-4
8-5
8-6
9-2
9-3
9-4
9-5
9-7
9-8
9-9
9-11

INTRODUCTION
The HAL MCEM-8080 Microcomputer System is a single printed-circuit
board computer that can be used for program development or for specific
control applications. The MCEM-8080 is designed around the Intel 8080A
single chip, 8-bit, N-channel microprocessor integrated circuit. The
MCEM-8080 printed circuit board contains the microprocessor IC,- its timing
and control circuitry. both Read Only Memory (ROM) and Random Access
Memory (RAM) integrated circuitry, and timing and control for Input / Out-
put (I/O) interfacing. Other accessories such as additional RAM, Keyboard/
Video Display unit, tape cassette memory, and power suppl ies can be used
with the basic MCEM circuit board. This manual discusses ONLY the basic
MCEM-BOBO board - the operation of the accessories is discussed in separate
manuals furnished with each unit.
The MCEM-8080A Microcomputer System manual is actually supplied in
two
publications: this MCEM-8080 Operating Manual, and the Intel 8080
Microcomputer Systems User1s Manual. Specific operating instructions
and specifications pertaining to the HAL Communications Corp. MCEM-8080
system are discussed in the MCEM-8080 Operating Manual. General information
relating to the 8080A and associated integrated circuits is discussed in
detail in the Intel 8080 Microcomputer Systems User's Manual (© Intel
Corporation). When pertinent, references are made in the operating manual
to the detailed discussions in the Intel manual. These referen~es are given
in the form: "Intel; pp A-xx to A-yy". In addition, a copy of the
Intel 8080 Assembly Language Reference Card (© Intel Corporation) is
furnished with the MCEM-8080 Microcomputer System to aid in program develop-
ment.
Figure 1. I MCEM-8080 Microcomputer System
iv

I. SYSTEM COMPONENTS
The HAL MCEM-8080 Microcomputer System contains the following basic
and optional components:
1.1 8080A Microprocessor
The 8080A is an eight bit microprocessor integrated circuit with
an instruction repertoire of 73 instructions. The execution time of
these instructions varies from 2.0 ~sec. to 9.0 ~sec. The 8080A integrated
circuit itself contains all of the circuitry required to address the memory,
address Input / Output (I/O) devices, and manipulate data. A more detailed
discussion of the 8080A will be found in pages 2-1 to 2-20 of the Intel
manual (Intel~. pp 2-1 to 2-20).
1.2 Processor Control Circuitry
Two additional integrated circuits are used in conjunction with the
808oA to provide all of the timing and control signals for the micro-'
processor system. These are the 8228 Bus Controller IC and the 8224 Clock
Generator IC.
1.2.1 8228 Bus Controller (Intel; pp 5-7 to 5-12)
A type 8228 integrated circuit is used to decode signals from the
8080A and generate the required bus control signals. This device also
buffers the 8080A data bus signals and will support a single vector
interrupt (RST 7).
1.2.2 8224 Clock Generator (Intel; pp 5-1 to 5-6)
A type 8224 integrated circuit generates all system timing signals.
An 18 MHz crystal is used with the device to generate the 2.0 MHz processor
timing signals, power-on reset signal and ready line synchronization pulses.
J.3 Random Access Memory
The standard MCEM circuit board is provided with 1024 bytes of Random
Access Memory (RAM). This memory can be used by the user's programs, but
the lower 64 bytes are required for the software monitor program. Additional
circuit board space is provided so that an additional 1024 bytes ("lK") of
RAM can be installed on the MCEM board (factory installation is recommended).
All
RAM integrated circuits should be type 8102A-4, a device featuring an
access time of 450 nsec. or less. Slower RAM devices should NOT be used as
they may cause improper operation of the system. Further information on the
8102A-4 is found on pages 5-79 through 5-82 of the Intel manual (Intel;
pp 5-79 to 5-82).
Within the processor memory space, the standard "IK" bytes of RAM
occupy locations between 0 and 1023 (0 - 3FF -Hex). The second (optional)
"IK" bytes of RAM occupy locations between 1024 and 2047 (400 H - 7FF H).
The software monitor uses RAM locations between 0 and 63 (0 - 3F H).
1-1

1.4 Read Only Memory
The MCEM system is provided with sufficient circuit board space for
4096 bytes of EPROM (Erasable Programmable Read Only Memory) or 2048 bytes
of bi-polar PROM (Programmable Read Only Memory - NOT erasable). The
device selection is made by selection of the proper circuit board jumpers.
Four socket locations are provided for the ROM - all four must be of the
same type (EPROM or PROM). The ROM occupies consecutive memory locations,
starting at 32,768 (8000 H).
1.4. I EPROM
Either a type 8708 or 8704 EPROM integrated circuit (Intel; pp 5-45 to
5-50) can be used on the MCEM board. The 8708 is a 1024 x 8 device and
the 8704 is a 512 x 8 device. Refer to Appendix A for proper jumper place-
ment.
1. 4.2 PROM
Type 3624 PROM integrated circuits can be used on the MCEM. This IC
is the standard device furnished with the MCEM. The 3624 is a bi-polar
PROM with a 512 x 8 organization. ' Up to four 3624 1s can be used on the
MCEM-8080 circuit board. NOTE: Production MCEM-8080 circuit boards are
jumpered for use of this device on the circuit board. If it is desired
to use other devices, refer to Appendix A for details.
1.4.3 ROM
A type 8308 ROM integrated circuit (Inte~; pp 5-59 & 5-60) can also be
used in
the HAL MCEM-8080. This is a mask-programmed version of the 8708.
Refer to Appendix A for jumper details.
1.4.4 Monitor Software ROM
The HAL software monitor can be resident in either 2-3624, 1-8708, or
l-83Q8 ROM integrated circuits. Either 2-3624 or 1-8308 ROM is standard
with the MCEM. The monitor software is 1024 bytes in length and begins at
location 32,768 (8000 H).
1.5 Serial Input / Output (I/O)
The standard MCEM-8080 provides for either synchronous or asynchronous
serial data interface. The software monitor supports asynchronous serial
I/O in either Baudot (5-unit) or ASCII (8-unit) codes.
1.5.1 8251 USART
A type 8251 integrated circuit (Intel; pp 5-135 to 5-146) Universal
Synchronous/Asynchronous Receiver/Transmitter (USART) is used to input and
output serial data. This device is fully programmable and is controlled by
the processor. Parallel-to-serial and serial-to-parallel conversions as
well as word length selection and parity are controlled by the 8251.
1-2

1.5.2 Serial Timing Oscillator
A type 555 integrated circuit timer is used to generate the serial
data baud rate. The data rate is screw-driver adjustable on the circuit
board. The actual 555 clock frequency is 4 times the baud rate in ASCI I
mode and 16 times the baud rate in Baudot mode.
1.5.3 EIA -RS-232C Data Interface
Two operational ampl ifiers (both halves of a type 145B Ie) are used
as RS-232 drivers and receivers. The serial output of the B251 USART is
directly converted to a ± 5 volt signal, with -5 volts representing the
"mark" signal condition and +5 volts as "space". The output impedance
of the circuit is approximately 400 ohms. For input data, an operational
amplifier is used as a sense ampl ifier and level converter. Input voltages
greater than +1.0 volts are interpreted to be in the "space
ll
condition and
those less than +1.0 volts as "mark". The input impedance is approximately
2700 ohms. This input will property sense TTL-level signals, as well as
EIA -RS-232C signals.
1.5.4 Current Loop Interface
Current loop signals with either 20 or 60 ma mark currents can also
be connected to the MCEM-BoBO. Two optical isolator integrated circuits
are ~sed to convert between the floating cur~ent loop circuit and the
RS-232 levels. These sensors are separated so that one can be used for
data input and the other for output (separate current loops - "full-
duplex" operation). The two circuits can also be series connected to
provide both data input and output on a single current loop circuit
("half-duplex" operation).
1.6 Parallel Data Input / Output
A type 8255 integrated circuit (Intel; pp 5-113 to 5-133) is provided
to allow parallel data interfacing. This device, called the "Programmable
Peripheral Interface
ll
, consists of three buffered B-bit parallel data ports.
The software monitor util izes the 8255 for parallel I/O operations.
1.7 Bus Indicators and Control
A number of indicators (small LEOs - Light Emitting Diodes) and switches
are installed along the front edge of the MCEM-BoBo circuit board to permit
evaluation and control of the processor operation.
1.7.1 Address Indicators
The entire 16 bits of the BOBo address bus are displayed on 16 LEDs.
The lamps are grouped in four-lamp clusters, four clusters total. Each
group
of four lamps represents a single hexadecimal (HEX) character, 0 through
F. An illuminated lamp indicates a logic "I" condition. Within a four-lamp
cluster, the least significant bit (LSB) is represented by the right-hand
lamp. Similarly, the right-hand cluster of four lamps represents the least
significant hexidecimal character.
1-3

1.7.2 Data Indication
Eight lamps (in two four-lamp clusters) are used to indicate the
state of the processor data bus. These lamps are immediately to the left
of the address lamps. As before, the right-hand lamp represents the LSB
and an illuminated lamp represents a logical 11111 for that bit.
1.7.3 Bus Control Indication
The four lamps on the extreme left end of the circuit board indicate
the state of the I/O Read, I/O Write, Memory Read, and Memory Write (left-
to-right order) signals from the processor. An illuminated lamp indicates
which of these operations is active. A complete description of the function
of these signals is found in the Intel manual (Intel; pp 5-7 to 5-12).
1.7.4 Manual Data Switches
Immediately in front of the eight data lamps are located two, four-
sectio~ miniature switches. The switches provide manual control of the
contents of the data bus. These switches can be used to enter data only
when the Data Bus Override (DBa) switch (to the right of the data switches)
is in the ON position. The data switch settings at any other time does
not affect the processor. The switches are arranged in the same manner as
the lamps, LSB to the right.
1.7.5 Run / Stop Switch
A miniature toggle switch on the right-hand section of the board
(labeled RUN - STOP) allows manual control of the 8080A Ready line. When
this switch is set to the RUN position, the processor will continue to
operate (unless halted by the program or some other control). When in the
STOP position, the processor is halted and only the manual STEP and RESET
switches will cause processor activity.
1.7.6 Reset Switch
The far right-hand push-button switch (labeled RESET) is a momentary
contact type that can be used to manually reset the 808oA. A reset operation
causes the program counter to set to zero and the interrupt flip-flop to be
cleared. Processor execution commences at location 0000 when the reset switch
is released. Appl ication of DC power supplies automatically issues a reset
function.
1.7.7 Single Step Switch
The STEP switch (located between the RUN - STOP and RESET switches)
allows manual stepping of the computer, one MEMORY cycle at a time. This
switch only functions when the processor has been halted by either the
RUN - STOP switch or the break point register. It is important to remember
that some instructions require more than one memory cycle and therefore more
than one operation of step switch to complete.
1-4

1.7.8 Break Point Register Switches
In the middle of the control area of the circuit board are located
four, four-section miniature switches. These 16 switches form a. "break
point register
l
•. Circuitry is provided to compare the value of this switch
register with the address bus and cause the 8080A to stop operation if the
two are equal. This function is similar to a programmable stop. Once the
808oA is halted due to a break point Ilmatch
ll
, it can only be caused to
continue running by either manual stepping with the STEP switch or by re-
setting the break point switches to a new value.
1.7.9 Memory Write and Output Write Switches
Two momentary switches are located on the far left-hand side of the
circuit board. These switches allow manual operation of memory or output
functions. The MEMORY WRITE switch will cause a manual memory write function
when depressed, overriding the normal bus control from the 8228 integrated
circuit. Similarly, depression of the OUTPUT WRITE switch will cause an
output write function, again overriding the normal control from the 8228.
1.8 Connectors used on the MCEM-8080
There are three connectors used on the basic MCEM-8080 circuit board.
These connectors are used for I/O Interface, Power Input, and connection
to the Universal Processor Bus. Mating connectors for each are furnished
wi th the MCEM.
1.8.1 I/O Interface Connector
Input / Output (I/O) connections to the MCEM are made through a 36 pin
circuit board edge connector (0.156
11
finger spacing, 18 pin double readout)
located on the left edge of the board. All three parallel I/O ports of the
8255 are available on this connector as well as connections for serial data.
The form of serial data to be used is selected with circuit board jumpers.
1.8.2 Power Connector
Power connections to the MCEM are made through the 12 pin edge
connector (0.156
11
finger spacing 6 pin double readout) located in the
upper right-hand corner of the circuit board. The MCEM requires ± 12 volt
and +5 volt power supplies.
1.8.3 Universal ~rocessor Bus Connector
Direct connection to the computer address, data, and control 1 ines
can be made through the 40 pin Universal Processor Bus (UPB) connector
located in the lower right-hand corner of the board. A mating connector
and attached ribbon cable are supplied for use of this feature. Connection
of options such as additional memory and the Keyboard/Video Display unit
is made through the UPB connector.
1-5