IS80LV52 Datasheet, PDF (21/48 Pages) Integrated Silicon Solution, Inc – CMOS SINGLE CHIP LOW VOLTAGE 8-BIT MICROCONTROLLER

IS80LV52
IS80LV32
ISSI ^®
MULTIPROCESSOR COMMUNICATIONS
Modes 2 and 3 have a special provision for multiprocessor
communications. In these modes, nine data bits are
received, followed by a stop bit. The ninth bit goes into
RB8; then comes a stop bit. The port can be programmed
such that when the stop bit is received, the serial port
interrupt is activated only if RB8 = 1. This feature is
enabled by setting bit SM2 in SCON.
The following example shows how to use the serial
interrupt for multiprocessor communications. When the
master processor must transmit a block of data to one of
several slaves, it first sends out an address byte that
identifies the target slave. An address byte differs from a
data byte in that the ninth bit is 1 in an address byte and
0 in a data byte. With SM2 = 1, no slave is interrupted by
a data byte. An address byte, however, interrupts all
slaves, so that each slave can examine the received byte
and see if it is being addressed. The addressed slave
clears its SM2 bit and prepares to receive the data bytes
that follows. The slaves that are not addressed set their
SM2 bits and ignore the data bytes.
SM2 has no effect in Mode 0 but can be used to check the
validity of the stop bit in Mode 1. In a Mode 1 reception, if
SM2 = 1, the receive interrupt is not activated unless a
valid stop bit is received.
Baud Rates
The baud rate in Mode 0 is fixed as shown in the following
equation.
Mode 0 Baud Rate = ^{Oscillator Frequency}
12
The baud rate in Mode 2 depends on the value of the
SMOD bit in Special Function Register PCON. If SMOD
= 0 (the value on reset), the baud rate is 1/64 of the
oscillator frequency. If SMOD = 1, the baud rate is 1/32 of
the oscillator frequency, as shown in the following equation.
Using the Timer 1 to Generate Baud Rates
When Timer 1 is the baud rate generator, the baud rates
in Modes 1 and 3 are determined by the Timer 1 overflow
rate and the value of SMOD according to the following
equation.
Mode 1, 3
Baud Rate
=
2^SMOD
32
X (Timer 1 Overflow Rate)
The Timer 1 interrupt should be disabled in this application.
The Timer itself can be configured for either timer or
counter operation in any of its 3 running modes. In the
most typical applications, it is configured for timer operation
in auto-reload mode (high nibble of TMOD = 0010B). In
this case, the baud rate is given by the following formula.
Mode 1,3 ₌
Baud Rate
2^SMOD
Oscillator Frequency
X
32
12x [256-(TH1)]
Programmers can achieve very low baud rates with Timer
1 by leaving the Timer 1 interrupt enabled, configuring the
Timer to run as a 16-bit timer (high nibble of TMOD =
0001B), and using the Timer 1 interrupt to do a 16-bit
software reload.
Table 9 lists commonly used baud rates and how they can
be obtained from Timer 1.
Mode 2 Baud Rate = ^2SMOD x (Oscillator Frequency)
64
In the IS80LV51/31, the Timer 1 overflow rate determines
the baud rates in Modes 1 and 3. In the IS80LV52/32,
these baud rates can be determined by Timer 1, Timer 2,
or both (one for transmit and the other for receive).
Integrated Silicon Solution, Inc. — 1-800-379-4774
21
ADVANCE INFORMATION MC019-0A
10/01/98