ADUC816 Analog Devices, ADUC816 Datasheet - Page 51

• Manufacturer Part Number: ADUC816
• Description: Precision Analog Microcontroller: 1MIPS 8052 MCU + 8kB Flash + Dual 16-Bit ADC + 12-Bit DAC
• Manufacturer: Analog Devices

Specifications of ADUC816

• Mcu Core: 8052
• Mcu Speed (mips): 1.3
• Sram (bytes): 256Bytes
• Gpio Pins: 34
• Adc # Channels: 4

REV. A
8051-COMPATIBLE ON-CHIP PERIPHERALS
This section gives a brief overview of the various secondary periph-
eral circuits are also available to the user on-chip. These remaining
functions are fully 8051-compatible and are controlled via standard
8051 SFR bit definitions.
Parallel I/O Ports 0–3
The ADuC816 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; others are
multiplexed with an alternate function 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 is an 8-bit open drain bidirectional I/O port that is directly
controlled via the Port 0 SFR (SFR address = 80 hex). 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 that state,
Port 0 pins can be used as high impedance inputs. An external
pull-up resistor will be required on Port 0 outputs to force a
valid logic high level externally. Port 0 is also the multiplexed
low-order address and data bus during accesses to external pro-
gram or data memory. In this application it uses strong internal
pull-ups when emitting 1s.
Port 1 is also an 8-bit port directly controlled via the P1 SFR
(SFR address = 90 hex). The Port 1 pins are divided into two
distinct pin groupings.
P1.0 and P1.1 pins on Port 1 are bidirectional digital I/O pins with
internal pull-ups. If P1.0 and P1.1 have 1s written to them via the
P1 SFR, these pins are pulled high by the internal pull-up resis-
tors. In this state they can also be used as inputs; as input pins
being externally pulled low, they will source current because of
the internal pull-ups. With 0s written to them, both these pins
will drive a logic low output voltage (VOL) and will be capable of
sinking 10 mA compared to the standard 1.6 mA sink capa-
bility on the other port pins. These pins also have various
secondary functions described in Table XXI.
Pin
P1.0
P1.1
The remaining Port 1 pins (P1.2–P1.7) can only be configured
as Analog Input (ADC), Analog Output (DAC) or Digital Input
pins. 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.
Port 2 is a bidirectional port with internal pull-up resistors directly
controlled via the P2 SFR (SFR address = A0 hex). Port 2 pins
that have 1s written to them are pulled high by the internal pull-up
resistors and, in that state, they can be used as inputs. As inputs,
Port 2 pins being pulled externally low will source current because
of the internal pull-up resistors. Port 2 emits the high order
Table XXI. Port 1, Alternate Pin Functions
Alternate Function
T2 (Timer/Counter 2 External Input)
T2EX (Timer/Counter 2 Capture/Reload Trigger)
address bytes during fetches from external program memory
and middle and high order address bytes during accesses to the
16-bit external data memory space.
Port 3 is a bidirectional port with internal pull-ups directly
controlled via the P2 SFR (SFR address = B0 hex). Port 3 pins
that have 1s written to them are pulled high by the internal pull-
ups and in that state they can be used as inputs. As inputs, Port
3 pins being pulled externally low will source current because of
the internal pull-ups. Port 3 pins also have various secondary
functions described in Table XXII.
Pin
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
The alternate functions of P1.0, P1.1, and Port 3 pins can only be
activated if the corresponding bit latch in the P1 and P3 SFRs
contains a 1. Otherwise, the port pin is stuck at 0.
Timers/Counters
The ADuC816 has three 16-bit Timer/Counters: Timer 0,
Timer 1, and Timer 2. The Timer/Counter hardware has been
included on-chip to relieve the processor core of the overhead
inherent in implementing timer/counter functionality in soft-
ware. Each Timer/Counter consists of two 8-bit registers THx and
TLx (x = 0, 1 and 2). All three can be configured to operate
either as timers or event counters.
In “Timer” function, the TLx register is incremented every
machine cycle. Thus one can think of it as counting machine
cycles. Since a machine cycle consists of 12 core clock periods,
the maximum count rate is 1/12 of the core clock frequency.
In “Counter” function, the TLx register is incremented by a
1-to-0 transition at its corresponding external input pin, T0, T1,
or T2. In this function, the external input is sampled during
S5P2 of every machine cycle. When the samples show a high in
one cycle and a low in the next cycle, the count is incremented.
The new count value appears in the register during S3P1 of the
cycle following the one in which the transition was detected. Since
it takes two machine cycles (16 core clock periods) to recognize a
1-to-0 transition, the maximum count rate is 1/16 of the core
clock frequency. There are no restrictions on the duty cycle of
the external input signal, but to ensure that a given level is
sampled at least once before it changes, it must be held for a mini-
mum of one full machine cycle. Remember that the core clock
frequency is programmed via the CD0–2 selection bits in the
PLLCON SFR.
Table XXII. Port 3, Alternate Pin Functions
Alternate Function
RXD (UART Input Pin)
(or Serial Data I/O in Mode 0)
TXD (UART Output Pin)
(or Serial Clock Output in Mode 0)
INT0 (External Interrupt 0)
INT1 (External Interrupt 1)
T0 (Timer/Counter 0 External Input)
T1 (Timer/Counter 1 External Input)
WR (External Data Memory Write Strobe)
RD (External Data Memory Read Strobe)