Intel MCS 51 User Manual

8XC52/54/58 HARDWAREDESCRIPTION
Table 4. Timer 2 Operating Modes
RCLK + TCLK
cPlm
TR2
MODE
o
0 1
16-BitAuto-Reload
I
o
I
1
Ill
16-BitCapture
I
I
1
I
x
Ill
BaudRateGenerator
I
I
x I x
Iol
oft-l
I
CAPTURE MODE
In
the capture mode there are two options selected by
bit EXEN2 in T2CON. If EXEN2 = O,Timer 2 is a
16-bit timer or counter which upon overfiow sets bit
TF2 in T2CON. This bit can then be used to generate
an interrupt. If EXEN2 = 1, Timer 2 still does the
above, but with the added feature that a 1-to-Otran-
sition at external input T2EX eauaes the current value
in TH2 and ‘fZ2 to be captured into RCAP2H and
RCAP2L, respectively. In additio~ the transition at
T2EX esuaes bit EXF2 in T2CON to be set. The EXF2
bit, like TF2, ean generate an interrupt. The capture
mode is illustrated in Figure 1.
AUTO-RELOAD (Up or Down Counter)
Timer 2 can be programmedto count up or down when
contlgursd in its 16-bit auto-reload mode. This feature
is invoked by a bit named DCEN (Down Counter En-
able) located in the SFR T2MOD (see Table 5). Upon
reset the DCEN bit is set to Oso that Timer 2 wilf
default to count up. When DCEN is set, Timer 2 can
count up or down depending on the valueof the T2EX
pin.
Figure 2 shows Timer 2 automatically counting up
when DCEN = O.In this mode there are two options
selected by bit EXEN2 in T2CON. If EXEN2 = O,
Timer 2 counts up to OFFFFH and then sets the TF2
bit upon overflow. The overtlow also causes the timer
registers to be reloaded with the 16-bit value in
RCAP2H and RCAP2L. The values in RCAP2H and
RCAP2L are preset by software. If EXEN2 = 1, a
16-bitreload can be triggeredeither by an overfiow or
by a l-to-O transition at external input T2EX. This
transition also sets the EXF2 bit. Eoth the TF2 and
EXF2 bita ean generatean intemupt if enabled.
OJ
c/E =1
I CONTROL
TR2
-.m-..--
T2 PIN
LAt’l UKt.
I II
TRANSITION
OUECTION
piaiim I +
TIMER2
INTERRUPT
T2EX PIN
+X1 ~
I
I CONTROL
EXEN2
2707S3-1
Figure1.Timer2inCaptureMode
4-6

Intel MCS 51 Specifications

General

Architecture	8-bit
Number of Instructions	111
Clock Speed	12 MHz
Register Size	8-bit
Internal RAM	128 bytes
Internal ROM	4 KB
External Memory	64 KB
I/O Pins	32
Timers	2
Serial Port	1
Interrupts	5
Operating Voltage	5V
UART	Yes
Program Memory	4 KB
RAM	128 bytes
Instruction Set	CISC

Summary

MCS® 51 Family of Microcontrollers Architectural Overview

THE MCS®-51 INSTRUCTION SET

Provides an overview of the MCS®-51 instruction set, optimized for 8-bit control applications.

Interrupt Structure

Overview of the 8051 interrupt structure, sources, and vectoring.

MCS® 51 Programmer’s Guide and Instruction Set

MCS®-51 INSTRUCTION SET

Provides a summary of the 8051 instruction set, including mnemonics and operands.

8051, 8052 and 80C51 Hardware Description

TIMER/COUNTERS

Describes Timer 0 and Timer 1, including operating modes and control registers.

8XC52/54/58 Hardware Description

8XC51FX Hardware Description

PORT STRUCTURES AND OPERATION

Details port structures, I/O configurations, and external memory access.

SERIAL INTERFACE

Covers serial port modes, framing error detection, and baud rate generation.

87C51GB Hardware Description

SPECIAL FUNCTION REGISTERS

Provides a map of the SFR space and their reset values.

I/O PORTS

TIMERS/COUNTERS

PROGRAMMABLE COUNTER ARRAY

SERIAL PORT

Details the serial port's modes, framing error detection, and baud rates.

INTERRUPTS

Covers interrupt sources, enable registers, and priority levels.

RESET

83C152 HARDWARE DESCRIPTION

GLOBAL SERIAL CHANNEL

DMA OPERATION

INTERRUPT STRUCTURE