Why are there no 74LS60-74LS70 为什么没有74ls60-74ls70

The 74LS series of integrated circuits does indeed have a gap between 74LS60 and 74LS70. This is primarily due to historical reasons in how these logic families were developed and numbered.
74LS系列集成电路确实在74LS60和74LS70之间存在空隙，不连续编号。这主要是由于这些逻辑家族是如何发展和编号的历史原因。

The main reasons for this gap include:造成这一断层的主要原因包括：

1. Number reservation: Some numbers were reserved for potential future designs that were never produced编号预留：一些编号是为未来从未生产过的潜在设计预留的

2. Obsolete designs: Some numbers were assigned to prototype designs that never made it to production or were quickly discontinued过时的设计：一些编号被分配给从未投入生产或很快停产的原型设计

3. Merged numbering systems: The 74xx series inherited numbering schemes from earlier logic families, and not all numbers were filled sequentially合并编号系统：74xx系列继承了早期逻辑家族的编号方案，并非所有数字都是按顺序填充的

4. Marketing decisions: Sometimes gaps were left to allow for design revisions or variants营销决策：有时会留出空白，以便进行设计修改或变体

The 74LS series follows the numbering scheme established by the original 7400 TTL series, and both have various gaps throughout their numbering sequence, not just between 60 and 70.

74LS系列遵循原始7400 TTL系列建立的编号方案，两者在整个编号序列中都有各种间隙，而不仅仅是60到70之间。