User`s guide

LZ87010 Advance User’s Guide Introduction
1/15/03 1-11
1.6.8 I/O Ports
Nine 8-bit ports can be assigned to up to 72 of the LZ87010’s 100 pins. Seven of these
ports provide general-purpose I/O functions on all pins. Two provide high-current outputs.
Most I/O ports are dual-purpose and have both a dedicated function (such as TXD0, the
Transmit Data output of UART 0) and a generalized I/O function (such as P3[1]).
The read/write ports contain weak internal pull-up resistors with a nominal value of 90 k
Ω.
When a ‘1’ bit is written, the port is driven strongly HIGH for one cycle, then tri-stated. This
drives the signal HIGH more quickly than is possible with a weak pull-up alone. The pull-
up then maintains the HIGH state. When a ‘0’ bit is written to a port, it is driven LOW con-
tinuously. The port should be written with ‘1’ bits before being used in read mode to place
the port in a high-impedance state.
The output-only ports (PORT 2 and PORT 9) are driven continuously in both the HIGH and
LOW output states. Reads from these registers return the last value written.
1.6.9 UARTs
The LZ87010 contains two general-purpose serial interfaces: UART 0 and UART 1. Both
are 8051-compatible. UART 1 adds a dedicated internal baud-rate generator.
1.6.10 I
2
C Interface
A two-wire serial interface provides master and slave communications using the industry-
standard I
2
C protocol, in both standard mode (100 kbit/s) and fast mode (400 kbit/s).
1.6.11 Analog Inputs (ADC)
Analog-to-digital conversion is provided for eight analog inputs, with 12-bit resolution over
the range of 0 to 3.3 V. The analog input section consists of an 8-input analog MUX, an
analog voltage reference input pin, and a single ADC with sample-and-hold.
Analog-to-digital conversions are initiated under software control, and a status bit reports
when the conversion is complete. A separate ADC clock divider allows the ADC unit to
operate at a different frequency from the core.
1.6.12 Analog Outputs (DACs) and Waveform Generators
Two identical 8-bit digital-to-analog converters, DAC 0 and DAC 1, provide analog outputs.
Each DAC has a 128 byte waveform RAM that can provide output waveforms of any
desired shape. Programmable indexing, clocking, and interrupt generation make this func-
tion extremely flexible. The waveform generators can be bypassed when direct access to
the DAC is desirable. The two DACs share a voltage reference input that sets the max-
imum output voltage.