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 method for controlling a plurality of memory devices comprising:
supplying a mode register command and a mode signal in common to the plurality of memory devices;
supplying a first enable signal having a first logic level to a first memory device of the plurality of memory devices, the first enable signal being supplied with a predetermined latency after supplying the mode register command and the mode signal; and
supplying a second enable signal having a second logic level to a second memory device of the plurality of memory devices, the second signal being supplied with the predetermined latency after supplying the mode register command and the mode signal;
wherein the mode register command is decoded and delayed by a latency shifter in each of the plurality of memory devices, the mode signal is written to a first mode register of the first memory device, and the mode signal is not written to a first mode register of the second memory device.
2. The method as claimed in claim 1 wherein the predetermined latency comprises a write latency.
3. The method as claimed in claim 1 wherein the predetermined latency comprises an additive latency.
4. The method as claimed in claim 1 wherein the predetermined latency comprises a write latency and an additive latency.
5. The method as claimed in claim 1 wherein the mode signal is supplied to address terminals of the plurality of memory devices.
6. The method as claimed in claim 1 wherein the first and second enable signals are supplied to data terminals of respective memory devices.
7. The method as claimed in claim 1 wherein the first logic level is a low logic level and the second logic level is a high logic level.
8. The method as claimed in claim 1 further comprising supplying a plurality of selection signals in common to the plurality of memory devices, wherein the first and second memory devices comprise a plurality of respective mode registers in addition to respective first mode registers and the plurality of selection signals selects the first mode registers.
9. The method as claimed in claim 8 wherein the selection signals are supplied to bank address terminals of the plurality of memory devices.
10. The method as claimed in claim 8 wherein the selection signals are encoded selection signals.
11. The method as claimed in claim 1 further comprising supplying a first chip select signal having an active state in common to the first and second memory devices, supplying a second chip select signal having an inactive state in common to third and fourth memory devices of the plurality of memory devices, supplying the first enable signal to the third memory device, and supplying the second enable signal to the fourth memory device, wherein the mode signal is not written to a first mode register of the third memory device and a first mode register of the fourth memory device.
12. The method as claimed in claim 11 wherein the active state is a high logic level and the inactive state is a low logic level.