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参数资料
| 型号： | 935263358512 |
| 厂商： | NXP SEMICONDUCTORS |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 8-BIT, OTPROM, 20 MHz, MICROCONTROLLER, PDSO20 |
| 封装： | 7.50 MM, SO-20 |
| 文件页数： | 8/58页 |
| 文件大小： | 312K |
| 代理商： | 935263358512 |
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Philips Semiconductors
Preliminary specification
87LPC764
Low power, low price, low pin count (20 pin)
microcontroller with 4 kB OTP
2000 Jun 01
13
Checking ATN and DRDY
When a program detects ATN = 1, it should next check DRDY. If
DRDY = 1, then if it receives the last bit, it should capture the data
from RDAT (in I2DAT or I2CON). Next, if the next bit is to be sent, it
should be written to I2DAT. One way or another, it should clear
DRDY and then return to monitoring ATN. Note that if any of ARL,
STR, or STP is set, clearing DRDY will not release SCL to high, so
that the I2C will not go on to the next bit. If a program detects
ATN = 1, and DRDY = 0, it should go on to examine ARL, STR,
and STP.
ARL
“Arbitration Loss” is 1 when transmit Active was set, but
this device lost arbitration to another transmitter.
Transmit Active is cleared when ARL is 1. There are
four separate cases in which ARL is set.
1. If the program sent a 1 or repeated start, but another
device sent a 0, or a stop, so that SDA is 0 at the rising
edge of SCL. (If the other device sent a stop, the setting
of ARL will be followed shortly by STP being set.)
2. If the program sent a 1, but another device sent a
repeated start, and it drove SDA low before SCL
could be driven low. (This type of ARL is always
accompanied by STR = 1.)
3. In master mode, if the program sent a repeated start,
but another device sent a 1, and it drove SCL low
before this device could drive SDA low.
4. In master mode, if the program sent stop, but it could
not be sent because another device sent a 0.
STR
“STaRt” is set to a 1 when an I2C start condition is
detected at a non-idle slave or at a master. (STR is not
set when an idle slave becomes active due to a start
bit; the slave has nothing useful to do until the rising
edge of SCL sets DRDY.)
STP
“SToP” is set to 1 when an I2C stop condition is
detected at a non-idle slave or at a master. (STP is not
set for a stop condition at an idle slave.)
MASTER
“MASTER” is 1 if this device is currently a master on
the I2C. MASTER is set when MASTRQ is 1 and the
bus is not busy (i.e., if a start bit hasn’t been
received since reset or a “Timer I” time-out, or if a stop
has been received since the last start). MASTER is
cleared when ARL is set, or after the software writes
MASTRQ = 0 and then XSTP = 1.
Writing I2CON
Typically, for each bit in an I2C message, a service routine waits for
ATN = 1. Based on DRDY, ARL, STR, and STP, and on the current
bit position in the message, it may then write I2CON with one or
more of the following bits, or it may read or write the I2DAT register.
CXA
Writing a 1 to “Clear Xmit Active” clears the Transmit
Active state. (Reading the I2DAT register also does this.)
Regarding Transmit Active
Transmit Active is set by writing the I2DAT register, or by writing
I2CON with XSTR = 1 or XSTP = 1. The I2C interface will only drive
the SDA line low when Transmit Active is set, and the ARL bit will
only be set to 1 when Transmit Active is set. Transmit Active is
cleared by reading the I2DAT register, or by writing I2CON with CXA
= 1. Transmit Active is automatically cleared when ARL is 1.
IDLE
Writing 1 to “IDLE” causes a slave’s I2C hardware to
ignore the I2C until the next start condition (but if
MASTRQ is 1, then a stop condition will cause this
device to become a master).
CDR
Writing a 1 to “Clear Data Ready” clears DRDY.
(Reading or writing the I2DAT register also does this.)
CARL
Writing a 1 to “Clear Arbitration Loss” clears the ARL bit.
CSTR
Writing a 1 to “Clear STaRt” clears the STR bit.
CSTP
Writing a 1 to “Clear SToP” clears the STP bit. Note that
if one or more of DRDY, ARL, STR, or STP is 1, the low
time of SCL is stretched until the service routine
responds by clearing them.
XSTR
Writing 1s to “Xmit repeated STaRt” and CDR tells the
I2C hardware to send a repeated start condition. This
should only be at a master. Note that XSTR need not
and should not be used to send an “initial”
(non-repeated) start; it is sent automatically by the I2C
hardware. Writing XSTR = 1 includes the effect of
writing I2DAT with XDAT = 1; it sets Transmit Active
and releases SDA to high during the SCL low time.
After SCL goes high, the I2C hardware waits for the
suitable minimum time and then drives SDA low to
make the start condition.
XSTP
Writing 1s to “Xmit SToP” and CDR tells the I2C
hardware to send a stop condition. This should only be
done at a master. If there are no more messages to
initiate, the service routine should clear the MASTRQ
bit in I2CFG to 0 before writing XSTP with 1. Writing
XSTP = 1 includes the effect of writing I2DAT with
XDAT = 0; it sets Transmit Active and drives SDA low
during the SCL low time. After SCL goes high, the I2C
hardware waits for the suitable minimum time and then
releases SDA to high to make the stop condition.
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