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buildtips:components_compatibility_and_substitution [2015/10/31 02:30]
martin8bity 		buildtips:components_compatibility_and_substitution [2016/07/06 00:09] (current)
davidcary mention other possible substitutions?
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 Most of N8VEM and related projects were designed with 74LS (low power Schottky transistor transistor logic) in mind. While this logic series is widely available, other alternatives exist, and can be used to substitute this logic series. Most of N8VEM and related projects were designed with 74LS (low power Schottky transistor transistor logic) in mind. While this logic series is widely available, other alternatives exist, and can be used to substitute this logic series.
  
-The two classes of logic, TTL and CMOS, are significantly different in their fundamental operation:  TTL is current driven, while CMOS is voltage driven.+The two classes of logic, TTL and CMOS, are significantly different in their fundamental operation: TTL is current driven, while CMOS is voltage driven.
  
 ===== TTL (Transistor Transistor Logic) ===== ===== TTL (Transistor Transistor Logic) =====
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 ==== 7400-series ==== ==== 7400-series ====
  
-The 7400 series was the original TTL logic series.  It was defined by a 16ma drive capability, and the necessity to sink 1.6ma at each input.  Hence, it had a fanout of 10, meaning that one gate could drive 10 inputs.  A typical gate delay for this series is about 10ns.+The 7400 series was the original TTL logic series. It was defined by a 16ma drive capability, and the necessity to sink 1.6ma at each input. Hence, it had a fanout of 10, meaning that one gate could drive 10 inputs. A typical gate delay for this series is about 10ns.
  
 ==== 7400 variants - 74H (high speed), 74L (low power) ==== ==== 7400 variants - 74H (high speed), 74L (low power) ====
  
-These families of TTL logic were never widely used.  The 74H series used even more power than the 7400 series, and the 74L series, although requiring less power, was quite a bit slower.+These families of TTL logic were never widely used. The 74H series used even more power than the 7400 series, and the 74L series, although requiring less power, was quite a bit slower.
  
 ==== 74S - Shottky TTL ==== ==== 74S - Shottky TTL ====
  
-Shottky logic replaced the 74H series.  It uses a great deal of power, all chips run hot, but it is very fast.  Typical gate delays are around 3ns, output drive around 20ma, and input sink current requirement of around 2ma.  Hence it has a fanout of 10.  Until the introduction of 74F logic, the 74S series was the choice where sheer speed was the consideration.+Shottky logic replaced the 74H series. It uses a great deal of power, all chips run hot, but it is very fast. Typical gate delays are around 3ns, output drive around 20ma, and input sink current requirement of around 2ma. Hence it has a fanout of 10. Until the introduction of 74F logic, the 74S series was the choice where sheer speed was the consideration.
  
 ==== 74LS - Low power Schottky TTL ==== ==== 74LS - Low power Schottky TTL ====
  
-Power requirements were greatly reduced with the introduction of 74LS logic.  Although drive capability was reduced to about 8ma, the input current sink requirement was greatly reduced to around 0.4ma.  Hence, LS-TTL has a fanout of about 20.  Speed is comparable to the 7400 series, a typical gate delay is about 10ns.  It essentially replaced the 7400 series.+Power requirements were greatly reduced with the introduction of 74LS logic. Although drive capability was reduced to about 8ma, the input current sink requirement was greatly reduced to around 0.4ma. Hence, LS-TTL has a fanout of about 20. Speed is comparable to the 7400 series, a typical gate delay is about 10ns. It essentially replaced the 7400 series.
  
 The 74LS series has for many years been one of the most widely used logic series. The 74LS series has for many years been one of the most widely used logic series.
- 
-====   ==== 
  
 ==== 74ALS - Advanced low power Schottky TTL ==== ==== 74ALS - Advanced low power Schottky TTL ====
  
-74ALS is one of the best replacements for 74LS.  It is about twice as fast as 74LS, typical gate delays being about 5ns.  Drive capability is the same, around 8ma, but the winning characteristic is the input current sink requirement of no more than 0.1ma. <font 12.8px/inherit;;inherit;;inherit>Normally 74ALS can be used as a drop-in replacement.</font> +74ALS is one of the best replacements for 74LS. It is about twice as fast as 74LS, typical gate delays being about 5ns. Drive capability is the same, around 8ma, but the winning characteristic is the input current sink requirement of no more than 0.1ma. <font 12.8px/inherit;;inherit;;inherit>Normally 74ALS can be used as a drop-in replacement.</font>
- +
-====   ====+
  
 ==== 74F - Fast TTL (or F = Fairchild) ==== ==== 74F - Fast TTL (or F = Fairchild) ====
  
-The 74F series, originally introduced by Fairchild Semiconductor, is about as fast as 74S logic, but consumes just a little more power than 74LS.  Typical gate delays are in the 3-4ns range, output drive is about 20ma, and the input sink current requirement is about 0.6ma.  For high speed, it has largely replaced the 74S series.+The 74F series, originally introduced by Fairchild Semiconductor, is about as fast as 74S logic, but consumes just a little more power than 74LS. Typical gate delays are in the 3-4ns range, output drive is about 20ma, and the input sink current requirement is about 0.6ma. For high speed, it has largely replaced the 74S series.
  
-==== <font inherit/ ;;inherit;;inherit>** 74AS - Advanced Schottky TTL **</font>   ====+==== ** 74AS - Advanced Schottky TTL ** ====
  
-This series was introduced as an alternative to 74F logic.  Just as 74ALS was a lower power version of 74LS logic, 74AS is a lower power version of 74S logic.+This series was introduced as an alternative to 74F logic. Just as 74ALS was a lower power version of 74LS logic, 74AS is a lower power version of 74S logic.
  
 ==== Substituting for 74LS ==== ==== Substituting for 74LS ====
  
-74ALS lowers power requirements, and is less expensive from many suppliers.  74F is the choice if speed is really needed.  Any of these families may be substituted if you run out of a particular 74LS part.+74ALS lowers power requirements, and is less expensive from many suppliers. 74F is the choice if speed is really needed. Any of these families may be substituted if you run out of a particular 74LS part.
  
-One caution:  74LS is often the only family with hysteresis on bus <font inherit/inherit;;inherit;;inherit>receiver</font> inputs.  This makes 74LS14, 74LS132, 74LS240, 74LS244, 74LS245, 74LS682, and 74LS688 the preferred chips for bus receivers.  As drivers, any of the above may be substituted.  One exception to this rule is 74ALS14 -- it has hysteresis on its inputs.+One caution: 74LS is often the only family with hysteresis on bus receiver inputs. This makes 74LS14, 74LS132, 74LS240, 74LS244, 74LS245, 74LS682, and 74LS688 the preferred chips for bus receivers. As drivers, any of the above may be substituted. One exception to this rule is 74ALS14 – it has hysteresis on its inputs.
  
-However, the N8VEM ECB bus seems <font inherit/inherit;;inherit;;inherit>not</font> to suffer from noise problems, and I have not heard of anyone having problems with substitutions for bus receivers.+However, the N8VEM ECB bus seems not to suffer from noise problems, and I have not heard of anyone having problems with substitutions for bus receivers.
  
 ===== CMOS (Complementary Metal-Oxide-Semiconductor) Logic ===== ===== CMOS (Complementary Metal-Oxide-Semiconductor) Logic =====
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   * 74LS Series bus drivers and transceivers, such as 74LS240, 74LS241, 74LS244, 74LS245 have hysteresis inputs (basically Schmidt triggers on inputs), newer TTL series ICs, such as 74F and 74ALS, and CMOS 74HCT, 74AHCT, 74ACT don't have it. This feature should reduce noise (ringing) during signal switching. It is not clear though that this feature is important for relatively slow ECB bus. Most ISA systems (with similar timing and frequencies) use 74F buffers and transceivers without any problems.   * 74LS Series bus drivers and transceivers, such as 74LS240, 74LS241, 74LS244, 74LS245 have hysteresis inputs (basically Schmidt triggers on inputs), newer TTL series ICs, such as 74F and 74ALS, and CMOS 74HCT, 74AHCT, 74ACT don't have it. This feature should reduce noise (ringing) during signal switching. It is not clear though that this feature is important for relatively slow ECB bus. Most ISA systems (with similar timing and frequencies) use 74F buffers and transceivers without any problems.
 +
 +====== Programmable logic device ICs ======
 +
 +===== Simple programmable logic devices =====
 +
 +PAL, PLA, PLD, SPLD, etc.
 +Alas, many of them are one-time programmable.
 +Can the erasable-and-reprogrammable GAL and EEPLD devices be programmed to be backwards compatible?
 +
 +===== CPLD =====
 +
 +"Atmel and Altera CPLD Compatibility Notes" ([[builderpages:abingham:cpld-compatibility]])
 +
  
 ====== ASICs (Z80, Intel 8xxx, UART) ====== ====== ASICs (Z80, Intel 8xxx, UART) ======
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   * Maxim MAX232ACP (either 0.1 uF or 1 uF capacitors)   * Maxim MAX232ACP (either 0.1 uF or 1 uF capacitors)
   * Texas Instruments TRS202ECN (0.1 uF capacitors)   * Texas Instruments TRS202ECN (0.1 uF capacitors)
 +  * STMicroelectronics ST232CN/BN (either 0.1 uF or 1 uF capacitors)
 +  * Maxim MAX3232CPE (3×0.33 uF + 1×0.047 uF capacitors for 5.0V power or 4×0.1 uF for 3.3V)
  
 ====== Passive Components ====== ====== Passive Components ======
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 [[http://www.ti.com/lit/an/scla007a/scla007a.pdf|HCMOS Design Considerations]] - Texas Instruments [[http://www.ti.com/lit/an/scla007a/scla007a.pdf|HCMOS Design Considerations]] - Texas Instruments
 +
  
buildtips/components_compatibility_and_substitution.1446273057.txt.gz · Last modified: 2015/10/31 02:30 by martin8bity
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