IC80C32 Datasheet, PDF (23/48 Pages) Integrated Circuit Solution Inc – CMOS SINGLE CHIP 8-BIT MICROCONTROLLER

IC80C52
IC80C32
More About Mode 0
Serial data enters and exits through RXD. TXD outputs the
shift clock. Eight data bits are transmitted/received, with
the LSB first. The baud rate is fixed at 1/12 the oscillator
frequency.
Figure 15 shows a simplified functional diagram of the
serial port in Mode 0 and associated timing.
Transmission is initiated by any instruction that uses SBUF
as a destination register. The "write to SBUF" signal at
S6P2 also loads a 1 into the ninth position of the transmit
shift register and tells the TX Control block to begin a
transmission. The internal timing is such that one full
machine cycle will elapse between "write to SBUF" and
activation of SEND.
SEND transfer the output of the shift register to the alternate
output function line of P3.0, and also transfers SHIFT
CLOCK to the alternate output function line of P3.1. SHIFT
CLOCK is low during S3, S4, and S5 of every machine
cycle, and high during S6, S1, and S2. At S6P2 of every
machine cycle in which SEND is active, the contents of the
transmit shift register are shifted one position to the right.
As data bits shift out to the right, 0s come in from the left.
When the MSB of the data byte is at the output position of
the shift register, the 1 that was initially loaded into the ninth
position is just to the left of the MSB, and all positions to the
left of that contain 0s. This condition flags the TX Control
block to do one last shift, then deactivate SEND and set TI.
Both of these actions occur at S1P1 of the tenth machine
cycle after "write to SBUF."
Reception is initiated by the condition REN = 1 and
RI = 0. At S6P2 of the next machine cycle, the RX Control
unit writes the bits 11111110 to the receive shift register
and activates RECEIVE in the next clock phase.
RECEIVE enables SHIFT CLOCK to the alternate output
function line of P3.1. SHIFT CLOCK makes transitions at
S3P1 and S6P1 of every machine cycle. At S6P2 of every
machine cycle in which RECEIVE is active, the contents of
the receive shift register are shifted on position to the left.
The value that comes in from the right is the value that was
sampled at the P3.0 pin at S5P2 of the same machine
cycle.
As data bits come in from the right, 1s shift out to the left.
When the 0 that was initially loaded into the right-most
position arrives at the left-most position in the shift register,
it flags the RX Control block to do one last shift and load
SBUF. At S1P1 of the tenth machine cycle after the write
to SCON that cleared RI, RECEIVE is cleared and RI is set.
More About Mode 1
Ten bits are transmitted (through TXD), or received (through
RXD): a start bit (0), eight data bits (LSB first), and a stop
bit (1). On receive, the stop bit goes into RB8 in SCON. In
the IC80C52 the baud rate is determined by the Timer 1
overflow rate.
Figure 16 shows a simplified functional diagram of the
serial port in Mode 1 and associated timings for transmit
and receive.
Transmission is initiated by any instruction that uses SBUF
as a destination register.
The "write to SBUF" signal also loads a 1 into the ninth bit
position of the transmit shift register and flags the TX
control unit that a transmission is requested. Transmission
actually commences at S1P1 of the machine cycle following
the next rollover in the divide-by-16 counter. Thus, the bit
times are synchronized to the divide-by-16 counter, not to
the "write to SBUF" signal.
The transmission begins when SEND is activated, which
puts the start bit at TXD. One bit time later, DATA is
activated, which enables the output bit of the transmit shift
register to TXD. The first shift pulse occurs one bit time after
that.
As data bits shift out to the right, 0s are clocked in from the
left. When the MSB of the data byte is at the output position
of the shift register, the 1 that was initially loaded into the
ninth position is just to the left of the MSB, and all positions
to the left of that contain 0s. This condition flags the TX
Control unit to do one last shift, then deactivate SEND and
set TI. This occurs at the tenth divide-by-16 rollover after
"write to SBUF".
Reception is initiated by a 1-to-0 transition detected at
RXD. For this purpose, RXD is sampled at a rate of 16 times
the established baud rate. When a transition is detected,
the divide-by-16 counter is immediately reset, and 1FFH is
written into the input shift register. Resetting the divide-by-
16 counter aligns its rollovers with the boundaries of the
incoming bit times.
The 16 states of the counter divide each bit time into 16th.
At the seventh, eighth, and ninth counter states of each bit
time, the bit detector samples the value of RXD. The value
accepted is the value that was seen in at least two of the
three samples. This is done to reject noise. In order to reject
false bits, if the value accepted during the first bit time is not
0, the receive circuits are reset and the unit continues
looking for another 1-to-0 transition. If the start bit is valid,
it is shifted into the input shift register, and reception of the
rest of the frame proceeds.
As data bits come in from the right, 1s shift to the left. When
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