PACE 1757 M/ME
SIGNAL DESCRIPTIONS (Continued)
BUS CONTROL
Mnemonic
Name
Description
TEST ON
System Test Enable
An active-LOW input, used to enable the execution of the System Test
builtinto theP1754, immediatelyaftercompletetionofthePACE1750A/
AE initialization and before fetching any instructions from the user's
program.
TEST END
System Test End
An active-HIGH output indicating whether the PACE 1754 System Test
hasbeencompleted. WhenevertheSystemTestisdisabledbytheTEST
ON signal, the TEST END output will be at a logical "1" immediately after
reset is removed.
SC -SC
System Configuration Inputs which are buffered onto IB0-IB4 when executing an I/O Read
0
4
Inputs
from I/O address 8410 (hex).
D/I
Data or instruction
Anoutputsignalthatindicateswhetherthecurrentbuscycleaccessisfor
Data (HIGH) or Instruction (LOW). It is three-state during bus cycles not
assigned to the CPU. This line can be used as an additional memory
address bit for systems that require separate data and program memory.
R/W
M/IO
Read or write
An output signal that indicates direction of data flow with respect to the
current bus master. A HIGH indicates a read or input operation and a
LOWindicatesawriteoroutputoperation. Thesignalisthree-stateduring
bus cycles not assigned to the CPU.
Memory or I/O
An output signal that indicates whether the current bus cycle is memory
(HIGH) or I/O (LOW). This signal is three-state during bus cycles not
assigned to the CPU.
RDYA_IN
Address ready In
An active HIGH input to the CPU that can be used to extend the address
phase of a bus cycle. When RDYA_IN is not active, wait states are
insertedbytheP1750A/AEtoaccomodateslowermemoryorI/Odevices.
ThislineisusuallyconnectedtoRDYA_OUTunlessthememoryinterface
logic requires the two RDYA signals remain discrete as an input and
output.
RDYA_OUT
RDYD
Address Ready Out
Data ready
An active HIGH output from the COMBO that indicates that there are no
wait states requested when STRBA is active. Wait states are inserted
whenthissignalbecomesinactiveduringSTRBA. Upto3waitstatescan
be inserted by programming an internal register. Three wait states are
inserted after reset (default).
An active HIGH signal to the CPU from the PIC that extends the data
phase of a bus cycle. When RDYD is not active, wait states are inserted
by the P1750A/AE to accomodate slower memory or I/O devices.
Do c um e nt # MICRO-10 REV B
Pa g e 23 o f 34
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