CDP1805 Intersil Corporation, CDP1805 Datasheet - Page 13

• Manufacturer Part Number: CDP1805
• Description: CMOS 8-Bit Microprocessor with On-Chip RAM and Counter/Timer
• Manufacturer: Intersil Corporation

The Counter/Timer has the following five programmable
modes:
1. Event Counter 1: Input to counter is connected to the EF1
2. Event Counter 2: Input to counter is connected to the EF2
3. Timer: Input to counter is from the divide by 32 prescaler
4. Pulse Duration Measurement 1: Input to counter con-
5. Pulse Duration Measurement 2: Operation is identical to
RESET
RESET
RESET
terminal. The high-to-low transition decrements the
counter.
terminal. The high-to-low transition decrements the
counter.
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.
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.
Pulse Duration Measurement 1, except EF2 is used as
the gate input.
RET
DIS
CIE
CID
XID
XIE
S3
S
S
S
R
R
R
INTERRUPT
INTERRUPT
INTERRUPT
EXTERNAL
COUNTER
MASTER
ENABLE
ENABLE
ENABLE
(MIE)
(CIE)
(XIE)
FF
FF
FF
Q
Q
Q
FIGURE 6. INTERRUPT LOGIC CONTROL DIAGRAM
PULSE MODE EF1
PULSE MODE EF2
LDC COUNTER
CDP1805AC, CDP1806AC
EXTERNAL INT
UNDERFLOW
COUNTER
STOPPED
RESET
BCI
13
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
quency trimming capacitors, C
at terminals 1 and 39. For additional information on crystal
oscillators, see lCAN-6565.
MIE
XI
S
R
INTERRUPT
COUNTER
LATCH
(CIL)
TO BRANCH
LOGIC (BXI)
Q
CI
TO BRANCH
LOGIC (BCI)
IN
and C
OUT
, may be required
INTERRUPT
REQUESTS
typ). Fre-