HS-80C85RH
Pin Description (Continued)
PIN
SYMBOL
NUMBER
TYPE
DESCRIPTION
INTR
10
I
Interrupt Request: Is used as a general purpose interrupt. It is sampled only during the next to
the last clock cycle of an instruction and during Hold and Halt states. If it is active, the Program
Counter (PC) will be inhibited from incrementing and an INTA will be issued. During this cycle a
RESTART or CALL instruction can be inserted to jump to the interrupt service routine. The INTR
is enabled and disabled by software. It is disabled by Reset and immediately after an interrupt is
accepted.
INTA
11
O
I
Interrupt Acknowledge: Is used instead of (and has the same timing as) RD during the Instruc-
tion cycle after an INTR is accepted. It can be used to activate an 8259A Interrupt chip or some
other interrupt port.
RST 5.5
RST 6.5
RST 7.5
9
8
7
Restart Interrupts: These three inputs have the same timing as INTR except they cause an
internal RESTART to be automatically inserted.
The priority of these interrupts is ordered as shown in Table 6. These interrupts have a higher
priority than INTR. In addition, they may be individually masked out using the SIM instruction.
TRAP
6
I
I
Trap: Trap interrupt is a non-maskable RESTART interrupt. It is recognized at the same time as
INTR or RST 5.5-7.5. It is unaffected by any mask or Interrupt Enable. It has the highest priority
of any interrupt. (See Table 6.)
RESET IN
36
Reset In: Sets the Program Counter to zero and resets the Interrupt Enable and HLDA flip-flops.
The data and address buses and the control lines are 3-stated during RESET and because of
the asynchronous nature of RESET the processor’s internal registers and flags may be altered
by RESET with unpredictable results. RESET IN is a Schmitt-triggered input, allowing connec-
tion to an R-C network for power-on RESET delay (see Figure 1). Upon power-up, RESET IN
must remain low for at least 10 “clock cycle” after minimum VDD has been reached. For proper
reset operation after the power-up duration, RESET IN should be kept low a minimum of three
clock periods. The CPU is held in the reset condition as long as RESET IN is applied.
RESET OUT
3
O
Reset Out: Reset Out indicates cpu is being reset. Can be used as a system reset. The signal
is synchronized to the processor clock and lasts an integral number of clock periods.
X1
X2
1
2
I
O
X1 and X2: Are connected to a crystal, LC, or RC network to drive the internal clock generator.
X, can also be an external clock Input from a logic gate. The input frequency is divided by 2 to
give the processor’s internal operating frequency.
CLK
SID
37
5
O
I
Clock: Clock output for use as a system clock. The period of CLK is twice the X1, X2 input
period.
Serial Input Data Line: The data on this line is loaded into accumulator bit 7 whenever a RIM
instruction is executed.
SOD
VCC
GND
4
O
I
Serial Output Data Line: The output SOD is set or reset as specified by the SlM instruction.
40
20
Power: +5V supply.
Ground: Reference.
I
RESET IN
R1
C1
VDD
TYPICAL POWER-ON RESET RC VALUES†
R1 = 75KΩ
C1 = 1µF
† Values may have to vary due to applied power supply ramp up time.
FIGURE 1. POWER-ON RESET CIRCUIT
Spec Number 518054
4
INTERSIL [ Intersil ]
