EVAL-ADUC831QSZ Datasheet, PDF (47/76 Pages) Analog Devices – MicroConverter®, 12-Bit ADCs and DACs with Embedded 62 kBytes Flash MCU

ADuC831
8052 COMPATIBLE ON-CHIP PERIPHERALS
This section gives a brief overview of the various secondary
peripheral circuits that are also available to the user on-chip.
These remaining functions are mostly 8052 compatible (with a
few additional features) and are controlled via standard 8052
SFR bit definitions.
Parallel I/O
The ADuC831 uses four input/output ports to exchange data
with external devices. In addition to performing general-purpose
I/O, some ports are capable of external memory operations while
others are multiplexed with alternate functions for the peripheral
features on the device. In general, when a peripheral is enabled,
that pin may not be used as a general-purpose I/O pin.
Port 0
Port 0 is an 8-bit, open-drain, bidirectional I/O port that is directly
controlled via the Port 0 SFR. Port 0 is also the multiplexed
low-order address and data bus during accesses to external pro-
gram or data memory.
Figure 36 shows a typical bit latch and I/O buffer for a Port 0
port pin. The bit latch (one bit in the port’s SFR) is represented
as a Type D flip-flop, which will clock in a value from the inter-
nal bus in response to a “write to latch” signal from the CPU.
The Q output of the flip-flop is placed on the internal bus in
response to a “read latch” signal from the CPU. The level of the
port pin itself is placed on the internal bus in response to a
“read pin” signal from the CPU. Some instructions that read a
port activate the “read latch” signal, and others activate the
“read pin” signal. See the following Read-Modify-Write Instruc-
tions section for more details.
READ
LATCH
INTERNAL
BUS
ADDR/DATA
CONTROL
DQ
DV_DD
P0.x
PIN
WRITE
TO LATCH
CL Q
LATCH
READ
PIN
Figure 36. Port 0 Bit Latch and I/O Buffer
As shown in Figure 36, the output drivers of Port 0 pins are
switchable to an internal ADDR and ADDR/DATA bus by an
internal CONTROL signal for use in external memory accesses.
During external memory accesses the P0 SFR gets 1s written to it
(i.e., all of its bit latches become 1). When accessing external
memory, the CONTROL signal in Figure 36 goes high, enabling
push-pull operation of the output pin from the internal address or
data bus (ADDR/DATA line). Therefore, no external pull-ups are
required on Port 0 in order for it to access external memory.
In general-purpose I/O port mode, Port 0 pins that have 1s written
to them via the Port 0 SFR will be configured as “open drain”
and will therefore float. In this state, Port 0 pins can be used as
high impedance inputs. This is represented in Figure 36 by the
NAND gate whose output remains high as long as the CONTROL
signal is low, thereby disabling the top FET. External pull-up
resistors are therefore required when Port 0 pins are used as
general-purpose outputs. Port 0 pins with 0s written to them
will drive a logic low output voltage (V_OL) and will be capable of
sinking 1.6 mA.
Port 1
Port 1 is also an 8-bit port directly controlled via the P1 SFR.
Port 1 digital output capability is not supported on this device.
Port 1 pins can be configured as digital inputs or analog inputs.
By (power-on) default these pins are configured as analog
inputs, i.e., 1 written in the corresponding Port 1 register bit.
To configure any of these pins as digital inputs, the user should
write a 0 to these port bits to configure the corresponding pin as
a high impedance digital input.
These pins also have various secondary functions described in
Table XVII.
Table XVII. Port 1, Alternate Pin Functions
Pin
Alternate Function
P1.0
T2 (Timer/Counter 2 External Input)
P1.1
T2EX (Timer/Counter 2 Capture/Reload Trigger)
P1.5
SS (Slave Select for the SPI Interface)
READ
LATCH
INTERNAL
BUS
DQ
WRITE
TO LATCH
READ
PIN
CL Q
LATCH
TO ADC
P1.x
PIN
Figure 37. Port 1 Bit Latch and I/O Buffer
Port 2
Port 2 is a bidirectional port with internal pull-up resistors
directly controlled via the P2 SFR. Port 2 also emits the high
order address bytes during fetches from external program memory
and middle and high order address bytes during accesses to the
24-bit external data memory space.
As shown in Figure 38, the output drivers of Ports 2 are switchable
to an internal ADDR and ADDR/DATA bus by an internal
CONTROL signal for use in external memory accesses (as for
Port 0). In external memory addressing mode (CONTROL = 1)
the port pins feature push-pull operation controlled by the inter-
nal address bus (ADDR line). However, unlike the P0 SFR
during external memory accesses, the P2 SFR remains unchanged.
REV. 0
–47–