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ST92195 ST92T195 ST92E195 - TWO-CHANNEL I2C BUS INTERFACE (I2C)
I2C BUS INTERFACE (Cont’d)
FREQUENCY REGISTER (I2CFQR)
R241 - Read/Write
Register Page: 44
Reset Value: 0000 0000(00h)
Bits 7:6 = BUS_S[1:0]
I2C BUS Selection bits
These bits connect the I2C interface to one of the
two possible buses as described in Table 1.
Table 33. I2C bus selection
Bit 5 = FMEN
Fast Mode Enable bit
This bit enables or disables the fast mode for the
SCL bus frequency.
0: Standard Mode (up to 100 kHz).
1: Fast Mode (over 100 kHz)
Bit 4 = PP_DRV
Push-Pull Drive mode bit
This bit determines if the master drives the SCL/
SDA buses in push-pull mode or in normal mode.
This allows the master to send data to the slave at
a faster speed.
0: The push-pull drive mode is disabled
1: The push-pull drive mode is enabled. All “nor-
mal” bus frequencies are doubled with the only
exception that the push-pull drive mode is auto-
matically disabled when Q[3:0]=1110 or
Q[3:0]=1111 to yield an SCL frequency of 500
kHz or 800 kHz. Refer to Q[3:0] bit description.
Note: The master automatically switches tempo-
rarily to normal bus driving mode with active pull-
up disabled and SCL frequency reduced by factor
of 2 when receiving acknowledges or data from
the addressed slave.
Bit 3:0 = Q[3:0]
SCL clock frequency bits
These bits select the SCL clock frequency when
the interface works in master mode. In slave trans-
mitter mode, they can be used to adjust the setting
up time between the first data byte and the clock.
Refer to Table 2.
In push-pull mode, the frequency values present-
ed in the following table correspond to an approxi-
mate frequency assuming that :
– the first data bit is transferred at a lower frequen-
cy (clock stretching capability),
– the acknowledge bit is transferred at the slave
speed without push-pull mode,
– other data bits are transferred with a real period
250 ns shorter than the values indicated in this
table.
Using the spike filter will add an internal delay act-
ing as a period increase by 250-ns steps.
Table 34. SCL Clock Frequency Selection
* These values are not covered by the Philips I2C
specification
Notes:
– The maximum allowed frequency depends on
the state of the FMEN control bit (If PP_DRV=0,
standard mode: 100 KHz; fast mode: 666.6 kHz)
– All frequency values depend on the bus line load
(except push-pull mode).
– All above values are obtained with loads corre-
sponding to a rise time from 0 to 250 ns.
– Any higher rise time (especially in standard
mode) will increase the period of the bus line fre-
quency by 250-ns steps.
70
BUS_S0 BUS_S1 FMEN PP_DRV
Q3
Q2
Q1
Q0
BUS_S1
BUS_S0
Selected Bus
0
SCL1/SDA1
0
1
SCL2/SDA2
SCL BUS FREQUENCY (in kHz)
Q[3:0]
PP_DRV = 0
SCL max Frequency
PP_DRV = 1
SCL Frequency (kHz)
(period: +0/-250ns
0000
20.10
40.40
0001
30.53
61.54
0010
40.40
81.63
0011
50.63
102.56
0100
63.49
129.03
0101
72.73
148.15
0110
85.11
173.91
0111
102.56
210.53
1000
129.03
266.67
1001
173.91
363.64
1010
210.53
444.44
1011
266.67
444.44
1100
400.00
571.43
1101
444.44
666.67
1110
444.44*
666.67
1111
666.67*
666.67