PIC16CE625-04/SS Microchip Technology, PIC16CE625-04/SS Datasheet - Page 28

• Manufacturer Part Number: PIC16CE625-04/SS
• Description: IC MCU OTP 2KX14 EE COMP 20SSOP
• Manufacturer: Microchip Technology
• Series: PIC® 16Cr

Specifications of PIC16CE625-04/SS

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 4MHz
• Peripherals: Brown-out Detect/Reset, POR, WDT
• Number Of I /o: 13
• Program Memory Size: 3.5KB (2K x 14)
• Program Memory Type: OTP
• Eeprom Size: 128 x 8
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 3 V ~ 5.5 V
• Oscillator Type: External
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 20-SSOP
• For Use With: 309-1016 - ADAPTER 20-SSOP TO 18-DIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Data Converters: -
• Connectivity: -

PIC16CE62X
5.3
5.3.1
Any instruction which writes, operates internally as a
read followed by a write operation. The BCF and BSF
instructions, for example, read the register into the
CPU, execute the bit operation and write the result back
to the register. Caution must be used when these
instructions are applied to a port with both inputs and
outputs defined. For example, a BSF operation on bit5
of PORTB will cause all eight bits of PORTB to be read
into the CPU. Then the BSF operation takes place on
bit5 and PORTB is written to the output latches. If
another bit of PORTB is used as a bidirectional I/O pin
(i.e., bit0) and it is defined as an input at this time, the
input signal present on the pin itself would be read into
the CPU and re-written to the data latch of this
particular pin, overwriting the previous content. As long
as the pin stays in the input mode, no problem occurs.
However, if bit0 is switched into output mode later on,
the content of the data latch may now be unknown.
Reading the port register, reads the values of the port
pins. Writing to the port register writes the value to the
port latch. When using read modify write instructions
(i.e., BCF, BSF, etc.) on a port, the value of the port pins
is read, the desired operation is done to this value, and
this value is then written to the port latch.
Example 5-2 shows the effect of two sequential
read-modify-write instructions (i.e., BCF, BSF, etc.) on
an I/O port.
A pin actively outputting a Low or High should not be
driven from external devices at the same time in order
to change the level on this pin (“wired-or”, “wired-and”).
The resulting high output currents may damage
the chip.
FIGURE 5-7:
DS40182C-page 28
Instruction
RB<7:0>
Instruction
RB <7:0>
fetched
Fetched
PC
PC
I/O Programming Considerations
BI-DIRECTIONAL I/O PORTS
Q1
M OVW F PORTB
Q2
W rite to
PORTB
SUCCESSIVE I/O OPERATION
PC
Q3 Q4
Q1
MOVF PORTB, W
Read PORTB
MOVW F
Execute
PORTB
Q2
PC + 1
T
Q3 Q4
PD
Q1
Port pin
sampled here
Q2
PORTB, W
PC + 2
Execute
NOP
MOVF
Q3 Q4
EXAMPLE 5-2:
;
;
;
;
;
;
;
;
;
; Note that the user may have expected the pin
; values to be 00pp pppp. The 2nd BCF caused
; RB7 to be latched as the pin value (High).
5.3.2
The actual write to an I/O port happens at the end of an
instruction cycle, whereas for reading, the data must be
valid at the beginning of the instruction cycle
(Figure 5-7). Therefore, care must be exercised if a
write followed by a read operation is carried out on the
same I/O port. The sequence of instructions should
allow the pin voltage to stabilize (load dependent)
before the next instruction causes that file to be read
into the CPU. Otherwise, the previous state of that pin
may be read into the CPU rather than the new state.
When in doubt, it is better to separate these instruc-
tions with an NOP or another instruction not accessing
this I/O port.
Initial PORT settings:
PORTB<7:6> have external pull-up and are not
connected to other circuitry
Q1
BCF PORTB, 7
BCF PORTB, 6
BSF STATUS,RP0
BCF TRISB, 7
BCF TRISB, 6
Execute
Q2
PC + 3
NOP
NOP
SUCCESSIVE OPERATIONS ON I/O PORTS
Q3 Q4
READ-MODIFY-WRITE
INSTRUCTIONS ON AN
I/O PORT
Note:
This example shows write to PORTB
followed by a read from PORTB.
Note that:
Therefore, at higher clock frequencies,
a write followed by a read may be
problematic.
data setup time = (0.25 T
where T
T
to output valid.
PD
1999 Microchip Technology Inc.
= propagation delay of Q1 cycle
; 01pp pppp
; 10pp pppp
;
; 10pp pppp
; 10pp pppp
CY
PORTB<7:4> Inputs
PORTB<3:0> Outputs
PORT latch PORT pins
---------- ----------
= instruction cycle and
CY
11pp pppp
11pp pppp
11pp pppp
10pp pppp
- T
PD
)