Z80181 Datasheet, PDF (10/74 Pages) Zilog, Inc. – SMART ACCESS CONTROLLER (SAC™)

Zilog
SYSTEM CONTROL SIGNALS
Pin Name
ST
Pin Number
3
Input/Output, Tri-State
Out, Active 1
Z80181
SMART ACCESS CONTROLLER SAC^™
Function
Status. This signal is used with the /M1 and /HALT output
to decode the status of the CPU machine cycle. Note that
the /M1 output is affected by the status of the M1E bit in the
OMCR register. The following table shows
the status while M1E=1.
ST /HALT /M1
0
1
0
1
1
0
1
1
1
0
X
1
0
0
0
1
0
1
Operation
CPU Operation
(1st Opcode fetch)
CPU Operation
(2nd and 3rd Opcode fetch)
CPU Operation
(MC other than Opcode fetch)
DMA operation
HALT mode
SLEEP mode
(Incl. System STOP mode)
2-10
DS971800500