P87LPC768 NXP Semiconductors, P87LPC768 Datasheet - Page 25

• Manufacturer Part Number: P87LPC768
• Description: The P87LPC768 is a 20-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
Regarding Software Response Time
Because the P87LPC768 can run at 20 MHz, and because the I
interface is optimized for high-speed operation, it is quite likely that
an I
at a rising edge of SCL) and write I2DAT before SCL has gone low
again. If XDAT were applied directly to SDA, this situation would
produce an I
about this possibility because XDAT is applied to SDA only when
SCL is low.
Conversely, a program that includes an I
a long time to respond to DRDY. Typically, an I
on a flag-polling basis during a message, with interrupts from other
peripheral functions enabled. If an interrupt occurs, it will delay the
response of the I
about this very much either, because the I
SCL low time until the service routine responds. The only constraint
on the response is that it must not exceed the Timer I time-out.
Values to be used in the CT1 and CT0 bits are shown in Table 2. To
allow the I
oscillator frequency, compare the actual oscillator rate to the f OSC
max column in the table. The value for CT1 and CT0 is found in the
2002 Mar 12
Low power, low price, low pin count (20 pin) microcontroller
with 4 kB OTP 8-bit A/D, Pulse Width Modulator
I2CFG
2
C service routine will sometimes respond to DRDY (which is set
BIT
I2CFG.7
I2CFG.6
I2CFG.5
I2CFG.4
I2CFG.2, 3
I2CFG.1, 0 CT1, CT0
2
C bus to run at the maximum rate for a particular
2
C protocol violation. The programmer need not worry
Address: C8h
Bit Addressable
2
C service routine. The programmer need not worry
SYMBOL
MASTRQ
SLAVEN
TIRUN
CLRTI
—
SLAVEN
7
FUNCTION
Slave Enable. Writing a 1 this bit enables the slave functions of the I
MASTRQ are 0, the I
time-out.
Master Request. Writing a 1 to this bit requests mastership of the I
progress when this bit is changed from 0 to 1, action is delayed until a stop condition is detected. A
start condition is sent and DRDY is set (thus making ATN = 1 and generating an I
When a master wishes to release mastership status of the I
MASTRQ is cleared by an I
Writing a 1 to this bit clears the Timer I overflow flag. This bit position always reads as a 0.
Writing a 1 to this bit lets Timer I run; a zero stops and clears it. Together with SLAVEN, MASTRQ,
and MASTER, this bit determines operational modes as shown in Table 1.
Reserved for future use. Should not be set to 1 by user programs.
These two bits are programmed as a function of the CPU clock rate, to optimize the MIN HI and LO
time of SCL when this device is a master on the I
controls both of these parameters, and also the timing for stop and start conditions.
MASTRQ
2
C service routine may take
2
C hardware stretches the
6
2
C routine operates
Figure 11. I
CLRTI
5
2
C hardware is disabled. This bit is cleared to 0 by reset and by an I
2
C Configuration Register (I2CFG)
TIRUN
2
2
C
C time-out.
4
23
—
3
first line of the table where CPU clock max is greater than or equal
to the actual frequency.
Table 2 also shows the machine cycle count for various settings of
CT1/CT0. This allows calculation of the actual minimum high and
low times for SCL as follows:
SCL min high low time (in microseconds)
For instance, at an 8 MHz frequency, with CT1/CT0 set to 1 0, the
minimum SCL high and low times will be 5.25 s.
Table 2 also shows the Timer I timeout period (given in machine
cycles) for each CT1/CT0 combination. The timeout period varies
because of the way in which minimum SCL high and low times are
measured. When the I
at every SCL transition with a value dependent upon CT1/CT0. The
pre-load value is chosen such that a minimum SCL high or low time
has elapsed when Timer I reaches a count of 008 (the actual value
pre-loaded into Timer I is 8 minus the machine cycle count).
—
2
2
C. The time value determined by these bits
CT1
1
2
C, it writes a 1 to XSTP in I2CON.
2
C interface is operating, Timer I is pre-loaded
2
C bus. If a transmission is in
2
CT0
C subsystem. If SLAVEN and
0
Reset Value: 00h
2
C interrupt).
P87LPC768
6 * Min Time Count
CPU clock (in MHz)
2
C
Preliminary data
SU01157