C8051F120/1/2/3/4/5/6/7 C8051F130/1/2/3
252
Rev. 1.4
SFR Definition 18.12. P3MDOUT: Port3 Output Mode
18.2. Ports 4 through 7 (100-pin TQFP devices only)
All Port pins on Ports 4 through 7 can be accessed as General-Purpose I/O (GPIO) pins by reading and
writing the associated Port Data registers (See SFR Definition 18.13, SFR Definition 18.15, SFR Definition
18.17, and SFR Definition 18.19), a set of SFR’s which are both bit and byte-addressable. Note also that
the Port 4, 5, 6, and 7 registers are located on SFR Page F. The SFRPAGE register must be set to 0x0F to
access these Port registers.
A Read of a Port Data register (or Port bit) will always return the logic state present at the pin itself, regard-
less of whether the Crossbar has allocated the pin for peripheral use or not. An exception to this occurs
during the execution of a
read-modify-write
instruction (ANL, ORL, XRL, CPL, INC, DEC, DJNZ, JBC,
CLR, SETB, and the bitwise MOV write operation). During the
read
cycle of the
read-modify-write
instruc-
tion, it is the contents of the Port Data register, not the state of the Port pins themselves, which is read.
Note that at clock rates above 50 MHz, when a pin is written and then immediately read (i.e. a write instruc-
tion followed immediately by a read instruction), the propagation delay of the port drivers may cause the
read instruction to return the previous logic level of the pin.
18.2.1. Configuring Ports which are not Pinned Out
Although P4, P5, P6, and P7 are not brought out to pins on the 64-pin TQFP devices, the Port Data regis-
ters are still present and can be used by software. Because the digital input paths also remain active, it is
recommended that these pins not be left in a ‘floating’ state in order to avoid unnecessary power dissipa-
tion arising from the inputs floating to non-valid logic levels. This condition can be prevented by any of the
following:
1.
Leave the weak pullup devices enabled by setting WEAKPUD (XBR2.7) to a logic 0.
2.
Configure the output modes of P4, P5, P6, and P7 to “Push-Pull” by writing PnMDOUT = 0xFF.
3.
Force the output states of P4, P5, P6, and P7 to logic 0 by writing zeros to the Port Data regis-
ters: P4 = 0x00, P5 = 0x00, P6= 0x00, and P7 = 0x00.
18.2.2. Configuring the Output Modes of the Port Pins
The output mode of each port pin can be configured to be either Open-Drain or Push-Pull. In the Push-Pull
configuration, a logic 0 in the associated bit in the Port Data register will cause the Port pin to be driven to
GND, and a logic 1 will cause the Port pin to be driven to V
DD
. In the Open-Drain configuration, a logic 0 in
the associated bit in the Port Data register will cause the Port pin to be driven to GND, and a logic 1 will
cause the Port pin to assume a high-impedance state. The Open-Drain configuration is useful to prevent
contention between devices in systems where the Port pin participates in a shared interconnection in
which multiple outputs are connected to the same physical wire.
Bits7–0: P3MDOUT.[7:0]: Port3 Output Mode Bits.
0: Port Pin output mode is configured as Open-Drain.
1: Port Pin output mode is configured as Push-Pull.
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Reset Value
00000000
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
SFR Address:
SFR Page:
0xA7
F
Summary of Contents for C8051F12 Series
Page 2: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 2 Rev 1 4 NOTES ...
Page 104: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 104 Rev 1 4 NOTES ...
Page 112: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 112 Rev 1 4 NOTES ...
Page 176: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 176 Rev 1 4 ...
Page 184: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 184 Rev 1 4 NOTES ...
Page 197: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 Rev 1 4 197 NOTES ...
Page 198: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 198 Rev 1 4 ...
Page 210: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 210 Rev 1 4 NOTES ...
Page 218: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 218 Rev 1 4 NOTES ...
Page 234: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 234 Rev 1 4 NOTES ...
Page 258: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 258 Rev 1 4 NOTES ...
Page 272: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 272 Rev 1 4 NOTES ...
Page 286: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 286 Rev 1 4 NOTES ...
Page 308: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 308 Rev 1 4 NOTES ...
Page 340: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 340 Rev 1 4 NOTES ...
Page 348: ...C8051F120 1 2 3 4 5 6 7 C8051F130 1 2 3 348 Rev 1 4 NOTES ...