PIC16C432T-I/SS Microchip Technology, PIC16C432T-I/SS Datasheet - Page 24

• Manufacturer Part Number: PIC16C432T-I/SS
• Description: IC MCU CMOS 8BIT 20MHZ 2K 20SSOP
• Manufacturer: Microchip Technology
• Series: PIC® 16Cr

Specifications of PIC16C432T-I/SS

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: LIN (Local Interconnect Network)
• Peripherals: Brown-out Detect/Reset, POR, WDT
• Number Of I /o: 12
• Program Memory Size: 3.5KB (2K x 14)
• Program Memory Type: OTP
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 4.5 V ~ 5.5 V
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 20-SSOP
• For Use With: AC164029 - MODULE SKT PROMATEII 20DIP/SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Data Converters: -

PIC16C432
4.3
4.3.1
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 bi-directional 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 4-2 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 4-7:
DS41140B-page 22
Instruction
RB<7:0>
Instruction
RB <7:0>
fetched
Fetched
PC
PC
I/O Programming Considerations
BI-DIRECTIONAL I/O PORTS
Q1
MOVWF PORTB
MOVWF PORTB
Q2
Write to
PORTB
PC
Q3
SUCCESSIVE I/O OPERATION
Q4
Q1
MOVF PORTB, W
MOVF PORTB, W
Read PORTB
MOVWF
Execute
Execute
PORTB
Q2
MOVWF
PORTB
PC + 1
T
Q3
PD
Q4
Q1
Preliminary
Port pin
sampled here
Q2
PORTB, W
PORTB, W
PC + 2
Execute
Execute
NOP
MOVF
MOVF
NOP
Q3
Q4
EXAMPLE 4-2:
4.3.2
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 4-
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 volt-
age 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 instructions with a 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
;
;
;
;
; 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).
Q1
Execute
Execute
Q2
PC + 3
NOP
NOP
NOP
NOP
BCF PORTB, 7
BCF PORTB, 6
BSF STATUS,
RP0
BCF TRISB, 7
BCF TRISB, 6
Q3
SUCCESSIVE OPERATIONS ON I/O
PORTS
Q4
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.
READ-MODIFY-WRITE
INSTRUCTIONS ON AN
I/O PORT
data setup time = (0.25 T
where T
T
to output valid.
PD
2002 Microchip Technology Inc.
= propagation delay of Q1 cycle
PORTB<7:4> Inputs
PORTB<3:0> Outputs
PORT latch
------------------
; 01pp pppp
;10pp pppp
;
; 10pp pppp
; 10pp pppp
CY
= instruction cycle and
PORT pins
----------------
11pp pppp
11pp pppp
11pp pppp
10pp pppp
CY
- T
PD
)