R

EM6607

Copyright © 2005, EM Microelectronic-Marin SA

15

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7.2

PortB

Port B is a 4-bit general-purpose I/O port. Outputs on this port are high current outputs. Each bit PB(0:3) can be separately

configured by software to be either input or output by writing to the corresponding bit of the CIOPortB control register. The

PortB register is used to read data when in input mode and to write data when in output mode. On each terminal controlled

Pull-Up/Down resistor can be selected by metal option, which are active only when selected as input. Special case is when

we want to use internal Strong Pull-Up resistor also when PortB terminal is declared as N-channel open drain output and

internal Pull-Up resistor is used to pull up the output (not-controlled Pull-Up). This is a special option “sod” = strong Pull-Up

for Open drain- active all the time (when terminal is input or output).

Writing 0 to the corresponding bit in the CIOPortB register sets input mode. This results in a high impedance state with the

status of the pin being read from register PortB. Writing 1 to the corresponding bit in the CIOPortB register sets output

mode. Consequently the output terminal follows the status of the bits in the PortB register. At initial RESET the CIOPortB

register is set to 0, thus setting the port to input. Additionally, PB0 can also be used as a three-tone buzzer output. For

details see section 7, Buzzer.

7.2.1

PortB registers

Table 16.

PortB input/output status register - PortB

Bit

Name

Reset

R/W

Description

3

PB3

-

R/W

PB3 I/O data

2

PB2

-

R /W

PB2 I/O data

1

PB1

-

R/W

PB1 I/O data

0

PB0

-

R /W

PB0 I/O data

Table 17.

PortB Input/Output control register - CIOportB

Bit

Name

Reset

R/W

Description

3

CIOPB3

0

R/W

PB3 Input/Output select

2

CIOPB2

0

R/W

PB2 Input/Output select

1

CIOPB1

0

R/W

PB1 Input/Output select

0

CIOPB0

0

R/W

PB0 Input/Output select

PB[3:0]

Vdd

2Y

2N

Mask

option

Mask

option

0

Mask

option

1

Mask

option

3Y

3N

Mask

option

Mask

option

Sleep

PortB RD

PG

NG

OE

D

Port B

CIOportB

OEBsleepRes

Figure 8.

Port B

If metal mask option 3Y (Input blocked when Output) is used and port is declared as Output (CIOPortB = 1111b) the real

port information cannot be read directly. In this case no direct logic operations (like AND PortB) on Output ports are

possible. This logic operation can be made with an image of the Port saved in the RAM which we store after on the output

port. This is valid for PortB, PortC and PortD when declared as output and the metal Option 3Y is used. In the case of metal

option 3N selected direct logic operations on output ports are possible.

If OEBsleepRes bit in Option2 register is set to “1” (Output Hi-Z in SLEEP mode) the active Output will go tri-state when

the circuit goes into SLEEP mode. In the case of OEBsleepRes at “0”, output stays active also in the SLEEP mode.