ST7265X datasheet(53/166 Pages) STMICROELECTRONICS

53 / 166 page

ST7265x

53/166

I/O PORTS (Cont’d)

9.2.4 Bit manipulation on Open Drain Outputs

As mentioned in Section 9.2.2, software should

avoid using bit manipulation instructions on the DR

ways access it using byte instructions. If bit manip-

ulation is needed, the solution is to use a copy of

the DR register in RAM, change the bits (using

BRES or BCLR instructions for example) and copy

the whole byte into the DR register each time the

value has to be output on a port. This way, no bit

manipulation is performed on the DR register but

each bit of the DR register can be controlled sepa-

rately.

9.3 I/O PORT IMPLEMENTATION

The hardware implementation on each I/O port de-

pends on the settings in the DDR and OR registers

and specific feature of the I/O port such as ADC In-

put or true open drain.

Switching these I/O ports from one state to anoth-

er should be done in a sequence that prevents un-

wanted side effects. Recommended safe transi-

tions are illustrated in Figure 36 Other transitions

are potentially risky and should be avoided, since

they are likely to present unwanted side-effects

such as spurious interrupt generation.

Figure 36. Interrupt I/O Port State Transitions

The I/O port register configurations are summa-

rized as follows.

Port B (without Option Register)

PB[7:0]

Table 14. Port Configuration (with Option Register)

floating/pull-up

interrupt

INPUT

floating

(reset state)

INPUT

open-drain

OUTPUT

push-pull

OUTPUT

= DDR, OR

MODE

DDR

floating input

push-pull output

Port

Pin name

Input

Output

OR = 0

OR = 1

OR = 0

OR = 1

High-Sink

Port A

PA7:0

floating

with interrupt

open drain

push-pull

Port C

PC7:4

floating

with interrupt

push-pull

PC3:0

floating

with interrupt

push-pull

Yes

Port D

PD7:0

floating

with interrupt

open drain

push-pull

Port E

PE7:6

floating

open drain

push-pull

Yes

PE5

floating

with pull-up, if se-

lected by option

byte see Section

15.1)

open drain (with

pull-up, if select-

ed by option byte

see Section 15.1)

push-pull

Yes

PE4:3

floating

open drain

push-pull

PE2:0

floating

open drain

push-pull

Yes

Port F

PF6:4

floating

True open drain

Yes

PF3:2

floating

push-pull

PF1:0

floating

True open drain

Yes

ST7265X Datasheet(PDF) 53 Page - STMicroelectronics

ST7265X Datasheet(HTML) 53 Page - STMicroelectronics

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