EM78P257
OTP ROM
1st
CLK
2nd
CLK
11th
10th
CLK
CLK
CLK
Tpi
Tsci
Tsca
Tsdc
Tsdc
DATA
Parity Bit Stop bit
Start bit
Bit0~Bit7
If CLK is low (inhibit status), no data transmission occurs.
If CLK is high and DATA is low (request-to-send), data is updated. Data is received from the system
and no transmission is started by EM78A/B until CLK and DATA are both high. IF CLK and DATA
are both high, the transmission is ready. DATA is valid prior to the falling edge of CLK and beyond
the rising edge of CLK. During transmission, EM78P257A/B check for line contention by checking
for an inactive level on CLK at interval not to exceed 100u seconds. Contention occurs when the
system lowers CLK to inhibit EM78P257A/B output after EM78P257A/B has started a transmission.
If this occurs before the rising edge of the tenth clock, EM78P257A/B internally stores its buffer and
returns DATA and CLK to an active level. If the contention does not occur by the tenth clock, the
transmission is completed.
Following a transmission, the system inhibits EM78P257A/B by holding CLK low until it can service
the input or until the system receives a request to send a response from EM78P257A/B.
(3) Receiving DATA (from system to EM78P257A/B)
Inhibit
2nd
9th
10th
CLK
1st
CLK
11th
CLK
CLK
CLK
CLK
Tmca
Tmdc
Tmci
DATA
Bit0~Bit7
Parity Bit Stop bit Line Control Bit
Start bit
System first checks if EM78P257A/B is transmitting data. If transmitting, the system can override
the output by forcing CLK to an inactive level prior to the tenth clock. If EM78P257A/B transmission
is beyond the tenth clock, the system receives the data. If EM78P257A/B is not transmitting or if the
system choose to override the output, the system forces CLK to an inactive level for a period of not
less than 100us while preparing for output. When the system is ready to output start bit (0), it allows
CLK to go to active level. If request-to-send is detected, EM78P257A/B clocks 11 bits. Following
the tenth clock, EM78P257A/B checks for an active level on the DATA line, and if found, forces
This specification is subject to change without prior notice.
57
07.27.2004 (V1.4)
ELAN [ ELAN MICROELECTRONICS CORP ]
