EM6603
6.3 PortB
The EM6603 has one four bit general purpose I/O port. 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 Pull-Up/Down resistor can be selected by metal option which are active only when selected as input.
Input mode is set by writing 0 to the corresponding bit in the CIOPortB register. This results in a high
impedance state with the status of the pin being read from register PortB. Output mode is set by writing 1 to the
corresponding bit in the CIOPortB register. 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 an input. Additionally,
PB0 can also be used as a three tone buzzer output. For details see section 7.
6.4 PortB registers
Table 14.PortB input status register - PortB
Bit
Name
PB3
PB2
PB1
PB0
Reset
R/W
R/W
R /W
R/W
R /W
Description
PB3 I/O data
PB2 I/O data
PB1 I/O data
PB0 I/O data
3
-
-
-
-
2
1
0
Table 15.PortB Input/Output control register - CIOportB
Bit
Name
Reset
R/W
R/W
R/W
R/W
R/W
Description
3
CIOPB3
CIOPB2
CIOPB1
CIOPB0
0
0
0
0
PB3 Input/Output select
PB2 Input/Output select
PB1 Input/Output select
PB0 Input/Output select
2
1
0
Figure 7.Port B
If metal mask option 5Y (Input blocked when Output) is used and the port is declared as the 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 5Y is used. In the case of metal option 5N selected direct logic operations on output ports
are possible.
If metal mask option 6Y (Output Hi-Z in SLEEP mode) the active Output will go Tristate when the circuit goes
into SLEEP mode. In the case of 6N output stay active also in the SLEEP mode.
03/02 REV. G/439
11
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