Semiconductor device having PDA function
A method for writing a mode register in a semiconductor device, the method includes receiving a mode register command and a mode signal; generating a first mode register setting signal; delaying the first mode register setting signal in a first latency shifter to provide a second mode register setting signal; receiving a data signal in synchronization with the second mode register setting signal; and writing the mode signal to the mode register only if the received data signal has a first logic level.
1. A semiconductor device comprising:
a first external terminal receiving a command signal;
a second external terminal receiving a data signal;
a third external terminal receiving an address signal;
a command decoder configured to output a mode register setting signal based on the command signal;
a first delay circuit configured to receive the mode register setting signal and output a delayed mode register setting signal;
a first mode register configured to provide an enable signal; and
a second mode register configured to receive the delayed mode register setting signal and the address signal;
wherein contents of the second mode register are overwritten with the address signal on receiving the delayed mode register setting signal when the enable signal has a first logic level and the data signal has a second logic level.
2. The semiconductor device as claimed in claim 1 , wherein the command decoder disables the mode register setting signal if the enable signal has a logic level different than the first logic level.
3. The semiconductor device as claimed in claim 1 , wherein the first delay circuit is a latency shifter.
4. The semiconductor device as claimed in claim 1 , wherein the first delay circuit delays the mode register setting signal by a write latency delay.
5. The semiconductor device as claimed in claim 4 , wherein the write latency delay is the sum of a CAS write latency delay and an additive latency delay.
6. The semiconductor device as claimed in claim 1 , wherein the first logic level is a high logic level.
7. The semiconductor device as claimed in claim 1 , wherein the second logic level is a low logic level.
8. The semiconductor device as claimed in claim 1 , further comprising:
a fourth external terminal receiving a bank address signal;
wherein the contents of the second mode register are overwritten with the address signal on receiving the delayed mode register setting signal when the enable signal has the first logic level, the data signal has the second logic level, and the bank address signal has a third logic level.
9. The semiconductor device as claimed in claim 1 , further comprising:
a second delay circuit configured to receive a write signal from the command decoder and output a delayed write signal.
10. The semiconductor device as claimed in claim 9 , wherein the second delay circuit is a latency shifter.
11. The semiconductor device as claimed in claim 1 , wherein the first delay circuit is configured to receive a write signal from the command decoder and output a delayed write signal.
12. The semiconductor device as claimed in claim 1 , further comprising:
a second delay circuit configured to receive the address signal and provide a delayed address signal to the second mode register.
13. The semiconductor device as claimed in claim 12 , wherein the second delay circuit is a FIFO.
14. The semiconductor device as claimed in claim 1 , wherein the semiconductor device is a DRAM.