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ST7285C Datasheet(HTML) 24 Page - STMicroelectronics

Part No. ST7285C
Description  8-BIT MCU FOR RDS WITH 48K ROM, 3K RAM, ADC, TWO TIMERS, TWO SPIs, I2C AND SCI INTERFACES
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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ST7285C Datasheet(HTML) 24 Page - STMicroelectronics

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ST7285C
4 ON-CHIP PERIPHERALS
4.1 I/O PORTS
4.1.1 Introduction
Each I/O Port can contain up to 8 individually pro-
grammable I/Os. The MCU features seven 8-bit
Ports (A, B, C,... G) and one 6-bit-port (H). Each I/
O pin is dedicated to its main functionality, thus re-
ducing and simplifying its programmability.
The current chapter describes the generic I/O
structure used in the MCU.
All I/Os are based on a generic circuit, of which a
block diagram is given in Figure 13. In most cases
the functions are simplified, and several sub-
blocks may be missing (such as, for instance, the
analog switch on ports B to H or pull-up and inter-
rupt logic for most of the I/O ports). Some registers
may also be absent where their functionality is re-
dundant: it is therefore advisable to consult the
Memory Map in section1.3 and the pin description
in section 1.2 for proper use of any particular I/O.
Only ports C4, C5, D4, D5, F0, F1, F2, F3, G3 fea-
ture interrupt capability.
The following sub-section 4.1.2 contains generic
information on ST7 I/O ports. For information spe-
cific to this device, please refer to sub-section
4.1.3.
4.1.2 Generic I/O Features
The I/O ports offer the following generic features:
– inputs with Schmitt trigger
– analog inputs, when connected via internal mul-
tiplexer
– interrupt generation, maskable by software
– EMI compliance thanks to reduced noise radia-
tion due to lowered cross-current in push pull
mode and reduced input susceptibility. This fea-
ture is particularly relevant in RDS applications.
Each
generic I/O pin may be individually program-
mable by software as:
– input: no pull-up, no interrupt generation
– input: pull-up, no interrupt generation
– input: pull-up, interrupt generation
– input: pull-down, no interrupt generation
– output: push-pull
– output: open-drain, no pull-up
– output: open-drain, with pull-up
4.1.2.1 Port Registers
Each port may be associated with up to four regis-
ters:
– DATA REGISTER (DR)
Address 0000 0000 000x xx00b; always present.
– DATA DIRECTION REGISTER(DDR)
Address 0000 0000 000x xx01b; always present.
– OPTION REGISTER (OR)
Address 0000 0000 000x xx10b; depending on
I/O dedication.
– PULL-UP REGISTER (PUR)
Address 0000 0000 000x xx11b; depending on
I/O dedication.
These are not internal CPU registers and must be
accessed by reading and writing to the relevant
memory locations. Refer toTable 1 - Memory Map
for the respective addresses and reset values.
4.1.2.2 Functional Description
Each I/O pin may be programmed independently
as an analog input if the port features analog capa-
bilities, as a digital input or a digital output with var-
ious variants, using the corresponding register
bits. When programmed as a digital input, a pull-up
or a pull-down resistor can, if present, be activated
by software. Only when enabling the pull-up, can
an interrupt function be programmed by software.
When programmed as an output, the I/O pin can
be programmed to operate either in push-pull or in
open-drain mode.
The interrupts generated by a port (active low) are
“ORed” to a single interrupt line that can be routed
to a CPU interrupt.


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