Vector 4 - Page 40

VECTOR 4
TECHNICAL INFORMATION
1.2 HOW THE MICROPROCESSORS INTERFACE
WITH OTHER SUBSYSTEMS
Summary: The SBC hardware allows the Z80B and 8088-2
Microprocessors to operate singly or alternately. This section describes
the subsystems that are responsible for this system flexibility.
AL M Switehing Contral
This subsystem allows you to switeh computer operation between the Z80B and
the 8088-2 microprocessors. In this capacity the subsystem has output lines
generating the following signals.
80 ENBL| This signal is used to enable the Z80B Microprocessor MUX (<A6>).
During normal Z80B operation this signal is LOW on RESET.*
88 ENBL| This control signal enables the 8088-2 Microprocessor MUX and
assists in generation of externally generated IORQ and MREQ
signals. NOTE: The 8088-2 operates in the MIN Mode.**
BUSRQ] When active this signal stops the Z80B (puts lines in high impedance
state) allowing for the 8088-2 to use the Bus.
Other An input signal to the RESET Subsystem assures that on RESET the
system will operate using the Z80B.
Computer operation can be changed from the Z80B mode to the 8088 mode by
doing a Port In instruction through either port 0CH or 0DH. Returning to the
Z80B mode is accomplished by doing another Port In instruction to one of the
same ports. Executing a Port Out instruction to port 0CH or 0DH will
automatically reset the system resulting in the ports being cleared and the Z30B
running.
*
See the ZILOG Z-80-CPU, Z80A-CPU TECHNICAL MANUAL for more detailed
information on Z80 microprocessor.
** gSee the INTEL 8086 FAMILY USER'S MANUAL for more detailed information
on the 8088-2 microprocessor.
09-01-82
7200-0001
II1-11