PACE 1757 M/ME
SIGNAL DESCRIPTIONS (Continued)
BUS STROBES AND QUALIFIERS
Mnemonic
Name
Description
STRBA (note 1) Address Strobe
An active HIGH output that can be used to externally latch the contents
of IB(0:15) into the address latches of the PIC and MMU at the HIGH to
LOW transition of the strobe. The signal is tristate during bus cycles not
assigned to this CPU. It is issued by the CPU and input to the MMU and
PIC.
STRBD (note 2) Data Strobe
An active LOW output used to read or write data from the PIC as well as
to strobe data in memory and XIO cycles. This signal is tri-state during
bus cycles not assigned to this CPU. It is interconnected in the same
manner as STRBA.
MEMW
Memory Write
Strobe
An active LOW output produced in memory write cycles by the PIC.
MEMR
IOW
Memory Read Strobe An active LOW output produced by the P1754 in memory read cycles.
I/O Write Strobe
I/O Read Strobe
Strobe Enable
An active LOW output produced by the P1754 in output write cycles.
An active LOW output produced by the P1754 during input read cycles.
IOR
STRB EN
An active LOW input, enabling the active state of the address outputs of
the P1754 and the MEMR, MEMW, IOR and IOW outputs. When a logic
"1" (if enabled by bits EST and EAD of the control register) it will
correspondingly tri-state the above signals.
INTA
Interrupt Acknowledge An active LOW output produced during any interrupt sequence
Strobe
corresponding to an output write to address 1000 (Hex).
DMA ACK
DMA Acknowledge
An active HIGH input from the DMA controller to the P1753 which
indicates a DMA cycle. Used to select the DMA table in the BPU memory
for protection. For example, this could allow the DMA channel to update
the program which could be write protected from the processor. In the
physical DMA mose, it will cause the Extended Address Liones (EXT
ADR )tobecomeinputsprovidingBPUprotectionoftheDMAtransfers.
0-7
EX RDY
External Data Ready
An active HIGH output from the MMU that indicates no wait states are
requested. It becomes inactive for one clock (inserting one wait state)
wheneveramemorypagedifferentthanthecurrentoneisaccessed(e.g.
a cache miss).
EX RDY1
External Data
Ready 1
An active LOW input to the PIC from the memory interface logic which at
a logical "1" overrides the internal RDYD generation and forces it to a
logical "0".
Note 1: One internal pulldown resistor is provided at the STRBA input. The nominal value is 40K Ohm and the maximum range is 20K Ohm to
80K Ohm. In designs with TTL devices loading STRBA, an additional external resistor may be required.
Note 2: One internal pullup is provided at the STRBD input. The nominal value is 40K Ohms and the maximum range is 20K-80K Ohms.
Do c um e nt # MICRO-10 REV B
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