There are 28 letters in the Lama orthography:
The Tonal System
Lama has two basic tones, a high tone and a low tone. These tones combine to give two contour tones, a falling tone and a rising tone. The latter is never realized phonetically. It always surfaces as a low tone. But when a low tone monosyllabic word follows a word with a final rising tone, the high part of that contour tone is then felt on that monosyllabic low tone word. This is explained by the general phenomenon of the high tone spread one syllable to the right found in most Gur languages [Kenstowicz et al. 1988]. The falling tone is only realized phonetically on the final syllable of a word (said in isolation). In phrase medial position, the falling tone simplifies to a level high tone; the delinked low part can cause a following high tone to be downstepped in specific environments [Kenstowicz et al. 1988].
Lama starts then with two basic tones which in turn combine to give two additional tones. The overall tone configurations are High, Low, High-Low, and Low-High in the underlying representation. At the surface level only the first three configurations are allowed.
Meterwa Akayhou Ourso, “Phonological processes in the noun class system of Lama,” Studies in African Linguistics Vol 20, No 2 (1989):154.