MA17501 Datasheet, PDF (7/35 Pages) Dynex Semiconductor – Radiation Hard MIL-STD-1750A Execution unit

3.2.6 Phase 2 Clock (CLK02N)
Output. CLK02N is used by the MA17502 Control Unit
(CU) in conjunction with CLKPCN to synchronize
microinstruction transmission on the M Bus to the
MAS281 machine cycle.
CLK02N cycles associated with MAS281 external
memory or l/O bus transactions are a minimum of five
OSC cycles in duration and are extended when wait
states are inserted via the RDYN input.
The high-to-low transition of CLK02N places the
upper 20 bits of a microinstruction on the external M Bus.
Wait states extend the trailing (based on SYNCN high-to-
low beginning the machine cycle) low state of CLK02N.
When PAUSEN or HLDAKN is low, CLK02N is held high.
CLK02N cycles associated with internal MAS281
operations are either five or six OSC cycles in duration.
Six OSC cycles are required for machine cycles
associated with microcode branches or with the
execution of internally (Interrupt Unit) decoded XlO
commands. Five OSC cycles are used for all other
internal operations, e.g., register to register transfers,
ALU functions, etc.
[NOTE: For MAS281s operating at high OSC
frequencies, the Interrupt Unit logic that creates IRDYN
may cause a wait state to be inserted during execution of
internal XlO commands. This would result in a CLK02N
cycle of seven OSC cycles duration.]
3.3 BUS CONTROL
This group of signals is provided to control Address/
Data (AD) bus transmissions (See Figure 4). The signals
indicate when address or data information is on the AD
Bus and what type of transaction is taking place during a
particular machine cycle.
3.3.1 Address Strobe (AS)
Output/Hi-z. AS high indicates that the Address/Data
(AD) Bus contains address information. The address
information is assured stable at the high-to-low transition
of this signal. ln this way, AS provides the necessary
control for a system Address Bus transparent latch
system interface.
The Interrupt Unit uses AS to extract the XlO
command information off the AD Bus for internally
decoded XlO commands, and the Memory Management
Unit/Block Protection Unit (MMU(BPU)) uses AS to
extract address information for memory management
and block protection functions, and to extract XlO
command information for MMU(BPU) decoded XlO
commands.
AS is placed in the high-impedance state during DMA
cycles by PAUSEN low and during the Hold state by
HLDAKN low. During internal non-AD Bus related CPU
operations, AS is held low for the entire machine cycle via
microcode control.
MA17501
Figure 4: Typical MAS281/MA17504 System Interface
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