Rainbow Electronics BR24C21FV User Manual

Page 6

BR24C21 / BR24C21F / BR24C21FJ / BR24C21FV

Memory ICs

(2) Bi-directional Mode
1) Bi-directional Mode and Recovery function

•The BR24C21, BR24C21F, BR24C21FJ and BR24C21FV can be switched from Transmit-Only Mode to
Bi-directional Mode by providing a valid high to low transition on the SCL pin, and the state of SDA is high-impedance.
•After a valid high to low transition on the SCL pin, the BR24C21, BR24C21F, BR24C21FJ and BR24C21FV begin to

count the VCLK clock. If the VCLK counter reaches 128 clock without the command for Bi-directional Mode, the
device revert to Transmit-Only Mode. (Recovery function) The VCLK counter is reset by providing a valid high to low
transition on the SCL pin. After reversion to Transmit-Only Mode, the devices begin to output a data with the 129th
rising clock edge on VCLK. The output data is 00h address data at the time.

•If the BR24C21, BR24C21F, BR24C21FJ and BR24C21FV are switched from Transmit-Only Mode and received

the command for Bi-directional Mode and responds with an Acknowledge, it is impossible to revert to Transmit-Only
Mode. (The only way to revert to Transmit-Only Mode is that the power down again.) Unless the input device code is
“1010”, the device responds no Acknowledge. If the VCLK counter reaches 128 clock afterward, it is possible to revert
to Transmit-Only Mode for Recovery function. If the master generates a stop condition during the slave address input,
it is possible to revert to Transmit-Only Mode.

•When the devices are switched from Transmit-Only Mode to Bi-directional Mode, the period of t

VHZ

need to be held.

Fig.12 RECOVERY MODE

ADDRESS 00h

SDA

VHZ

VCLK

MODE

Transmit-Only

Bi-directional
Transition Mode with possibility to return to Transmit-Only Mode

Transmit-Only

SCL

129

128

127

Fig.13 MODE CHANGE

SDA

VHZ

VCLK

MODE

Transmit-only

Bi-directional
Transition Mode with possibility to return to Transmit-Only Mode

Bi-directional
parmanently

SCL

R/W

ACK

∗

128