UPPERcase
For Model I with lower case installed
William R. Bell, El Granada, CA
If you have a lowercase modification in your TRS-80 Model I
Level II and a simple driver, you may find that you produce lowercase when you press the shift key with a letter. This is reverse from a typewriter, which normally will produce an uppercase letter when used with the shift key.
This hardware modification will give you a switch-selectable uppercase or lowercase when used with the shift key. The keys, other than letters and the @ key, are not affected. Two integrated circuits (IC's) are added to the keyboard.
The circuit is shown in Figure 1. The two NOR gates decode the keyboard and control the latch. The latch locks the shift keys in the inverted position (as if pressed) when a letter or the @ key is used and non-inverted position (not pressed) when any other key is pressed.
74LS74 Latch
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