參數(shù)資料
型號： 25C256
廠商： Microchip Technology Inc.
英文描述： 256K 5.0V SPI Bus Serial EEPROM(4.5~5.5V,256K位,SPI總線串行EEPROM)
中文描述： 256K 5.0V SPI總線串行EEPROM（4.5?5.5V的，256K位和SPI總線串行EEPROM的）
文件頁數(shù)： 36/170頁
文件大?。?/td> 4191K
代理商： 25C256
PIC16F62X
DS40300C-page 34
Preliminary
2003 Microchip Technology Inc.
TABLE 5-2:
SUMMARY OF REGISTERS ASSOCIATED WITH PORTA
(1)
5.2
PORTB and TRISB Registers
PORTB is an 8-bit wide bi-directional port. The
corresponding data direction register is TRISB. A '1' in
the TRISB register puts the corresponding output driver
in a Hi-impedance mode. A '0' in the TRISB register
puts the contents of the output latch on the selected
pin(s).
PORTB is multiplexed with the external interrupt,
USART, CCP module and the TMR1 clock input/output.
The standard port functions and the alternate port
functions are shown in Table 5-3. Alternate port
functions override TRIS setting when enabled.
Reading PORTB register reads the status of the pins,
whereas writing to it will write to the port latch. All write
operations are read-modify-write operations. So a write
to a port implies that the port pins are first read, then
this value is modified and written to the port data latch.
Each of the PORTB pins has a weak internal pull-up
(
≈
200
μ
A typical). A single control bit can turn on all the
pull-ups. This is done by clearing the RBPU
(OPTION<7>) bit. The weak pull-up is automatically
turned off when the port pin is configured as an output.
The pull-ups are disabled on Power-on Reset.
Four of PORTB’s pins, RB<7:4>, have an interrupt-on-
change feature. Only pins configured as inputs can
cause this interrupt to occur (i.e., any RB<7:4> pin con-
figured as an output is excluded from the interrupt-on-
change comparison). The input pins (of RB7:RB4) are
compared with the old value latched on the last read of
PORTB. The “mismatch” outputs of RB7:RB4 are
OR’ed together to generate the RBIF interrupt (flag
latched in INTCON<0>).
This interrupt can wake the device from SLEEP. The
user, in the interrupt service routine, can clear the
interrupt in the following manner:
a)
Any read or write of PORTB. This will end the
mismatch condition.
b)
Clear flag bit RBIF.
A mismatch condition will continue to set flag bit RBIF.
Reading PORTB will end the mismatch condition and
allow flag bit RBIF to be cleared.
This interrupt on mismatch feature, together with
software configurable pull-ups on these four pins allow
easy interface to a key pad and make it possible for
wake-up on key-depression. (See AN552)
The interrupt-on-change feature is recommended for
wake-up on key depression operation and operations
where PORTB is only used for the interrupt-on-change
feature. Polling of PORTB is not recommended while
using the interrupt-on-change feature.
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
POR
Value on
All Other
RESETS
05h
PORTA
RA7
RA6
RA5
RA4
RA3
RA2
RA1
RA0
xxxx 0000
xxxu 0000
85h
TRISA
TRISA7
TRISA6
TRISA5
TRISA4
TRISA3
TRISA2
TRISA1
TRISA0
1111 1111
1111 1111
1Fh
CMCON
C2OUT
C1OUT
C2INV
C1INV
CIS
CM2
CM1
CM0
0000 0000
0000 0000
9Fh
VRCON
VREN
VROE
VRR
—
VR3
VR2
VR1
VR0
000- 0000
000- 0000
Legend:
Note 1:
Shaded bits are not used by PORTA.
— = Unimplemented locations, read as ‘0’, u = unchanged, x = unknown
Note:
If a change on the I/O pin should occur
when a read operation is being executed
(start of the Q2 cycle), then the RBIF inter-
rupt flag may not get set.
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