HS-80C85RH
Basic System Timing
A machine cycle normally consists of three T states, with the
exception of OPCODE FETCH, which normally has either
four or six T states (unless WAIT or HOLD states are forced
by the receipt of READY or HOLD inputs). Any T state must
be one of ten possible states, shown in Table 11.
The HS-80C85RH has a multiplexed Data Bus. ALE is used
as a strobe to sample the lower 8-bits of address on the
Data Bus. Figure 15 shows an instruction fetch, memory
read and I/O write cycle (as would occur during processing
of the OUT instruction). Note that during the I/O write and
read cycle that the I/O port address is copied on both the
upper and lower half of the address.
TABLE 11. HS-80C85RH MACHINE STATE CHART
MA-
CHINE
STATUS & BUSES
CONTROL
There are seven possible types of machine cycles. Which of
these seven takes place is defined by the status of the three
status lines (lO/M, S1, S0) and the three control signals (RD,
WR, and INTA). (See Table 10.) The status lines can be
used as advanced controls (for device selection, for exam-
ple), since they become active at the T1 state, at the outset
of each machine cycle. Control lines RD and WR are used
as command lines since they become active when the trans-
fer of data is to take place.
STATE S1, S0 IO/M A8-15 AD0-7 RD,WR INTA ALE
T1
X
X
X
X
1
X
X
X
X
X
X
1
X
1
X
X
X
1
1
1
1
1
1
1†
0
T2
TWAIT
T3
X
X
X
X
0
X
X
X
X
0
T4
0††
0††
0††
TS
TS
TS
X
TS
TS
TS
TS
TS
TS
1
0
T5
1
X
1
0
TABLE 10. HS-80C85RH MACHINE CYCLE CHART
T6
1
X
1
0
STATUS
CONTROL
TRESET
THALT
THOLD
X
0
TS
TS
TS
TS
TS
TS
0
MACHINE CYCLE
Opcode Fetch (OF)
IO/M S1 S0 RD WR INTA
0
0
0
0
1
1
1
1
1
0
1
0
1
1
0
1
0
1
1
0
0
1
0
1
1
1
1
0
1
0
1
1
1
1
1
1
0
X
0
Memory Read (MR)
Memory Write (MW)
0 = Logic “0”
1 = Logic “1”
TS = High Impedance
X = Unspecified
I/O Read
I/O Write
(IOR)
(IOW)
† ALE not generated during 2nd and 3rd machine cycles of DAD
instruction.
†† IO/M = 1 during T4, T6 of INA machine cycle.
Acknowledge (INA)
of INTR
Bus Idle
(BI)
DAD
Ack. of
0
1
1
1
0
0
1
0
1
1
1
1
1
1
1
RST,
TRAP
HALT
TS
TS TS
M1
T3
M2
T2
M3
T2
T1
T2
T4
T1
T3
T1
T3
T
CLK
A8-A15
PCH (HIGH ORDER ADDRESS)
(PC + 1)H
IO PORT
PCL
(PC+1)L
IO PORT
AD0-7
ALE
(LOW ORDER DATA FROM
ADDRESS)
DATA TO
DATA FROM
MEMORY (I/O
PORT ADDRESS)
MEMORY
MEMORY OR
PERIPHERAL
(INSTRUCTION)
RD
WR
IO/M
STATUS
S1-S0 (FETCH)
10 (READ)
01 WRITE
11
FIGURE 15. 80C85RH BASIC SYSTEM TIMING
Spec Number 518054
16
INTERSIL [ Intersil ]
