PIC14000 datasheet(35/153 Pages) MICROCHIP

35 / 153 page

Preliminary

DS40122B-page 35

PIC14000

If the CMBOE bit (CMCON<5>) is set, the RD3/REFB

pin becomes the programmable reference B output

and pin RD2/CMPB becomes the comparator B output.

PORTD<1:0> also serve multiple functions. These pins

act as the I2C data and clock lines when the I2C module

is enabled.

The TRISD register controls the direction of the Port D

pins.

‘1’

each

location

conﬁgures

the

corresponding port pin as an input. Upon reset, this

tially inputs. The data register should be initialized prior

to conﬁguring the port as outputs.

Unused inputs should not be left floating to avoid

leakage currents. All pins have input protection diodes

to VDD and VSS.

EXAMPLE 5-3:

INITIALIZING PORTD

Note:

Setting CMBOE changes the deﬁnition of

RD3/REFB and RD2/CMPB, bypassing

the PORTD data and TRISD register set-

tings.

CLRF

PORTD

; Initialize PORTD data

;

latches before setting

;

the data direction

;

BSF

STATUS, RP0

; Select Bank1

MOVLW

0xFF

; Value used to initialize

; data direction

MOVWF

TRISD

; Set RD<7:0> as inputs

5.4

I/O Programming Considerations

5.4.1

BI-DIRECTIONAL I/O PORTS

Reading the port register reads the values of the port

pins. Writing to the port register writes the value to the

port latch. Some instructions operate internally as

read-modify-write. 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 PORTC will

cause all eight bits of PORTC to be read into the CPU.

Then the BSF operation takes place on bit5 and

PORTC is written to the output latches. If another bit of

PORTC is used as a bi-directional I/O pin (say 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.

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 (“wire-or”, “wire-and”).

The resulting high output currents may damage the

chip.

Example 5-4 shows the effect of two sequential read

modify write instructions (ex. BCF, BSF, etc.) on an I/O

Port.

EXAMPLE 5-4:

READ MODIFY WRITE

INSTRUCTIONS ON AN

I/O PORT

;

Initial PORT settings:

PORTC<7:4> Inputs

;

PORTC<3:0> Outputs

;

PORTC<7:6> have external pull-up and are not

connected to other circuitry

;

PORT

latch

PORT pins

;

----------

BCF PORTC, 7

; 01pp

pppp

11pp pppp

BCF PORTC, 6

; 10pp

pppp

11pp pppp

BSF STATUS,RP0

;

BCF TRISC, 7

; 10pp

pppp

11pp pppp

BCF TRISC, 6

; 10pp

pppp

10pp pppp

;

; Note that the user may have expected the pin

; values to be 00pp pppp. The 2nd BCF caused

; RC7 to be latched as the pin value (High).

PIC14000 Datasheet(PDF) 35 Page - Microchip Technology

PIC14000 Datasheet(HTML) 35 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL