CDP1805ACE datasheet(13/30 Pages) INTERSIL

13 / 30 page

The Counter/Timer has the following five programmable

modes:

1. Event Counter 1: Input to counter is connected to the EF1

terminal. The high-to-low transition decrements the

counter.

2. Event Counter 2: Input to counter is connected to the EF2

terminal. The high-to-low transition decrements the

counter.

3. Timer: Input to counter is from the divide by 32 prescaler

clocked by TPA. The prescaler is decremented on the

low-to-high transition of TPA. The divide by 32 prescaler

is reset when the counter is in a mode other than the

Timer mode, system RESET, or stopped by a STPC.

4. Pulse Duration Measurement 1: Input to counter con-

nected to TPA. Each low-to-high transition of TPA decre-

ments the counter if the input signal at EF1 terminal (gate

input) is low. On the transition of EF1 to the positive state,

the count is stopped, the mode is cleared, and the inter-

rupt request latched. If the counter underflows while the

input is low, interrupt will also be set, but counting will

continue.

5. Pulse Duration Measurement 2: Operation is identical to

Pulse Duration Measurement 1, except EF2 is used as

the gate input.

The modes can be changed without affecting the stored

count.

Those modes which use EF1 and EF2 terminals as inputs do

not exclude testing these flags for branch instructions.

The Stop Counter (STPC) instruction clears the counter

mode and stops counting. The STPC instruction should be

executed prior to a GEC instruction, if the counter is in the

Event Counter Mode 1 or 2.

In addition to the five programmable modes, the Decrement

Counter instruction (DTC) enables the user to count in soft-

ware. In order to avoid conflict with counting done in the

other modes, the instruction should be used only after the

mode has been cleared by a Stop Counter instruction.

The Enable Toggle Q instruction (ETQ) connects the Q-line

flip-flop to the output of the counter, such that each time the

counter decrements from 01 to its next value, the Q output

changes state. This action is independent of the counter

mode and the Interrupt Enable flip-flops. The Enable Toggle

Q condition is cleared by an LDC with the Counter/Timer

stopped, system Reset, or a BCl with Cl = 1.

NOTE: SEQ and REQ instructions are independent of ETQ, they

can SET or RESET Q while the Counter is running.

On-Board Clock (See Figure 8, Figure 9 and Figure 10)

Clock circuits may use either an external crystal or an RC

network.

A typical crystal oscillator circuit is shown in Figure 8. The

crystal is connected between terminals 1 and 39 (CLOCK

and XTAL) in parallel with a resistance, RF (1m

Ω typ). Fre-

quency trimming capacitors, CIN and COUT, may be required

at terminals 1 and 39. For additional information on crystal

oscillators, see lCAN-6565.

MASTER

INTERRUPT

ENABLE

(MIE)

RET

RESET

DIS

COUNTER

PULSE MODE EF1

UNDERFLOW

PULSE MODE EF2

BCI

RESET

LDC

• COUNTER

STOPPED

COUNTER

INTERRUPT

LATCH

(CIL)

COUNTER

INTERRUPT

ENABLE

(CIE)

CIE

RESET

CID

EXTERNAL

INTERRUPT

ENABLE

(XIE)

XIE

RESET

XID

INTERRUPT

REQUESTS

EXTERNAL INT

MIE

TO BRANCH

LOGIC (BXI)

TO BRANCH

LOGIC (BCI)

FIGURE 6. INTERRUPT LOGIC CONTROL DIAGRAM

CDP1805AC, CDP1806AC

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