interface CMOS with TTL

interfacing of cmos and ttl families

How do I interface TTL with CMOS logic? Do i need to interface between TTL families like LS with ALS etc.. ?

ttl to cmos interface

74HCT is compatible to standard TTL on in- and output. Other CMOS families, depends on ...

ttl interface

depend on...?

ttl cmos interface

voltage

Most ttl like the 74 hc als and ls are 5 volts some cmoss can be as high as 16 volts. So a current limiting resistor is needed.

interface cmos ttl

how about interfacing LS with other family in TTL series?

cmos to ttl interface

darrenbkl,
The output of a CMOS device is compatible with the input of a TTL device as long as the power supply voltages are the same. If you ty to drive the input of a CMOS gate from a TTL output you run into trouble. The reason is that worst case TTL "1" output level can be as low as 2.4 volts (with a 5V supply). This is close to the CMOS input switching threshold (with a 5V supply), so the result would be unpredictable. At best, you would have very low noise immunity in the "1" state.
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As FVM mentioned, 74HCT TTL is compatible with TTL. These CMOS devices are designed with a lower allowable logic "1" input voltage than standard CMOS.
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Regarding compatability of LSTTL with standard TTL, the two families are compatible. However, you must be careful with the "Fanout" of LSTTL. Most LSTTL gates can only drive 1 TTL load in the "0" state.
Regards,
Kral

interfacing cmos and ttl

ok thx for all the help. What is the difference between totem pole and open collector output?

cmos ttl interface

darrenbkl,
A totem pole output has active devices that provide low impedance drives for both the 1 state and the low state. The active "1" state driver is often refered to as a "pull-up" transistor. The active "0" state driver is often referred to as a "pull-down" transistor.
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An open collector (or drain) device has only the active pull-down device. When the device is in the 0 state, the output impedance is low. When in the 1 state, an open collector (or drain) provides an open circuit. This configuration is useful when you want to control a device that uses a different power supply voltage than the voltage of the gate itself. It can also be used in the "wired and" configuration in which the outputs of several open collector devices can be directly connected together. In this case an external resistor to the power supply is usually used. In this configuration, the output goes to one if and only iff the outputs of all the devices are driven to the "1" state.
Regards,
Kral