Rainbow Electronics T89C51IC2 User Manual
Page 7
7
T89C51IC2
Rev. C – 3-Dec-01
I/O
CEX4: Capture/Compare External I/O for PCA module 4
I/O
MOSI: SPI Master Output Slave Input line
When SPI is in master mode, MOSI outputs data to the slave peripheral. When SPI is
in slave mode, MOSI receives data from the master controller.
XTALA1
21
15
I
Crystal A 1: Input to the inverting oscillator amplifier and input to the internal clock
generator circuits.
XTALA2
20
14
O
Crystal A 2: Output from the inverting oscillator amplifier
XTALB1
2
40
I
Crystal B 1: (Sub Clock) Input to the inverting oscillator amplifier and input to the
internal clock generator circuits.
XTALB2
1
39
O
Crystal B 2: (Sub Clock) Output from the inverting oscillator amplifier
P2.0-P2.7
24-31
18-25
I/O
Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 pins that
have 1s written to them are pulled high by the internal pull-ups and can be used as
inputs. As inputs, Port 2 pins that are externally pulled low will source current because
of the internal pull-ups. Port 2 emits the high-order address byte during fetches from
external program memory and during accesses to external data memory that use 16-bit
addresses (MOVX @DPTR).In this application, it uses strong internal pull-ups emitting
1s. During accesses to external data memory that use 8-bit addresses (MOVX @Ri),
port 2 emits the contents of the P2 SFR. Some Port 2 pins receive the high order
address bits during EPROM programming and verification:
P2.0 to P2.5 for 16Kb devices
P2.0 to P2.6 for 32Kb devices
P3.0-P3.7
11,
13-19
5,
7-13
I/O
Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 pins that
have 1s written to them are pulled high by the internal pull-ups and can be used as
inputs. As inputs, Port 3 pins that are externally pulled low will source current because
of the internal pull-ups. Port 3 also serves the special features of the 80C51 family, as
listed below.
11
5
I
RXD (P3.0): Serial input port
13
7
O
TXD (P3.1): Serial output port
14
8
I
INT0 (P3.2): External interrupt 0
15
9
I
INT1 (P3.3): External interrupt 1
16
10
I
T0 (P3.4): Timer 0 external input
17
11
I
T1 (P3.5): Timer 1 external input
18
12
O
WR (P3.6): External data memory write strobe
19
13
O
RD (P3.7): External data memory read strobe
PI2.0-PI2.1
34, 12
28, 6
Port I2: Port I2 is an open drain. It can be used as inputs (must be polarized to Vcc
with external resistor to prevent any parasitic current consumption).
34
28
I/O
SCL (PI2.0): I2C Serial Clock
SCL output the serial clock to slave peripherals
SCL input the serial clock from master
12
6
I/O
SDA (PI2.1): I2C Serial Data
SDA is the bidirectional I2C data line
Mnemonic
Pin Number
Type
Name and Function
PLCC44
VQFP44 1.4