P87LPC760 NXP Semiconductors, P87LPC760 Datasheet - Page 34

• Manufacturer Part Number: P87LPC760
• Description: The P87LPC760 is a 14-pin single-chip microcontroller designed forlow pin count applications demanding high-integration, low costsolutions over a wide range of performance requirements
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Timer Overflow Toggle Output
Timer 0 can be configured to automatically toggle a port output
whenever a timer overflow occurs. The same device pins that is
used for the T0 count inputs are also used for the timer toggle
outputs. This function is enabled by control bit T0OE in the P2M1
register. The port outputs will be a logic 1 prior to the first timer
overflow when this mode is turned on.
UART
The P87LPC760 includes an enhanced 80C51 UART. The baud rate
source for the UART is timer 1 for modes 1 and 3, while the rate is
fixed in modes 0 and 2. Because CPU clocking is different on the
P87LPC760 than on the standard 80C51, baud rate calculation is
somewhat different. Enhancements over the standard 80C51 UART
include Framing Error detection and automatic address recognition.
The serial port is full duplex, meaning it can transmit and receive
simultaneously. It is also receive-buffered, meaning it can
commence reception of a second byte before a previously received
byte has been read from the SBUF register. However, if the first byte
still hasn’t been read by the time reception of the second byte is
complete, the first byte will be lost. The serial port receive and
transmit registers are both accessed through Special Function
Register SBUF. Writing to SBUF loads the transmit register, and
reading SBUF accesses a physically separate receive register.
The serial port can be operated in 4 modes:
Mode 0
Serial data enters and exits through RxD. TxD outputs the shift
clock. 8 bits are transmitted or received, LSB first. The baud rate is
fixed at 1/6 of the CPU clock frequency.
Mode 1
10 bits are transmitted (through TxD) or received (through RxD): a
start bit (logical 0), 8 data bits (LSB first), and a stop bit (logical 1).
When data is received, the stop bit is stored in RB8 in Special
Function Register SCON. The baud rate is variable and is
determined by the Timer 1 overflow rate.
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Low power, low price, low pin count (14 pin)
microcontroller with 1 kbyte OTP
31
uses SBUF as a destination register. Reception is initiated in Mode 0
Mode 2
11 bits are transmitted (through TxD) or received (through RxD):
start bit (logical 0), 8 data bits (LSB first), a programmable 9th data
bit, and a stop bit (logical 1). When data is transmitted, the 9th data
bit (TB8 in SCON) can be assigned the value of 0 or 1. Or, for
example, the parity bit (P, in the PSW) could be moved into TB8.
When data is received, the 9th data bit goes into RB8 in Special
Function Register SCON, while the stop bit is ignored. The baud
rate is programmable to either 1/16 or 1/32 of the CPU clock
frequency, as determined by the SMOD1 bit in PCON.
Mode 3
11 bits are transmitted (through TxD) or received (through RxD): a
start bit (logical 0), 8 data bits (LSB first), a programmable 9th data
bit, and a stop bit (logical 1). In fact, Mode 3 is the same as Mode 2
in all respects except baud rate. The baud rate in Mode 3 is variable
and is determined by the Timer 1 overflow rate.
In all four modes, transmission is initiated by any instruction that
by the condition RI = 0 and REN = 1. Reception is initiated in the
other modes by the incoming start bit if REN = 1
Serial Port Control Register (SCON)
The serial port control and status register is the Special Function
Register SCON, shown in Figure 31. This register contains not only
the mode selection bits, but also the 9th data bit for transmit and
receive (TB8 and RB8), and the serial port interrupt bits (TI and RI).
The Framing Error bit (FE) allows detection of missing stop bits in
the received data stream. The FE bit shares the bit position SCON.7
with the SM0 bit. Which bit appears in SCON at any particular time
is determined by the SMOD0 bit in the PCON register. If SMOD0 =
0, SCON.7 is the SM0 bit. If SMOD0 = 1, SCON.7 is the FE bit.
Once set, the FE bit remains set until it is cleared by software. This
allows detection of framing errors for a group of characters without
the need for monitoring it for every character individually.
P87LPC760
Preliminary data