R
EM3027
Calculation of external pull–up resistor
The following conditions have to be met:
Rise time is equal to 0.847RPU (CB + N * CI/O
)
⇒ RPU < tR max / (0.847 (CB + N CI/O)), where N is total number of
I/O pins connected to the corresponding bus line.
(tR in ns, C in pF, R in kΩ)
The minimum value of the pullup resistor value can be calculated with the IOL value of the SDA output:
RPU = (Vcc – VOL) / IOL
( IOL: see Table 7, page 5, Output Parameters; e.g. 5mA at VCC = 5.0V, with VOL = 0.8V )
Start
Stop
SDA
tBUF
tHIGH
tLOW
tR
SCL
tF
tSU:STO
tSU:STA
tHD:STA
tHD:DAT
tSU:DAT
Figure 8: I2C Timing
10.2 I2C Specification compliance
EM3027 device with I2C serial interface was designed
in compliance with Philips Semiconductors I2C-bus
specification UM10204 (Rev. 03 – 19 June 2007), Fast-
mode class (up to 400kbit/s). Device address consists
of 7 bits. Clock stretching is not supported.
There are, however, the following discrepancies between
I2C specification and EM3027 interface:
1) Falling time on SDA driven by EM3027 can be
shorter than 20 + 0.1* CB ns. (CB is total capacitive
load for SDA bus line in pF) In other words, slope
control of falling edges on SDA is missing.
Brief manual to I2C interface read and write
transmissions is to be found in §7.1.
2) Some timing parameters differ from the original I2C
specification – refer to Table 13.
Copyright © 2009, EM Microelectronic-Marin SA
12/09 – rev D
www.emmicroelectronic.com
23
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