The following content is taken from Wikipedia for reference only.
In Beijing Mandarin without Rusheng, Rusheng in the Middle Ages was classified into flat, rising and falling tones, which were called "Rusheng Tri-tones". There are several rules (with a few exceptions) on how to allocate.
1. Full-voiced initials are raised or dropped (such as thin and continuous silence).
2. The voiced consonants are voiced (e.g. weakened).
3. The unvoiced consonants may fall into any category of flat tone, rising tone, rising tone and falling tone, and there is no fixed rule.
A simple method for judging sound entry
When all the following same horizontal arrangement conditions are met, it is a tone-entering word (blank means unlimited); However, many input words do not meet the requirements of any of the following lines, such as "cut" and "tower", which need to be memorized.
Except for initials and finals.
ㄅ,,,, ㄐ, ㄓ, ㄗ(b,d,g,j,zh,z) Yang Pingbu,,, za, za.
ㄉ、ㄊ、ㄌ、ㄗ、ㄘ、ㄙ(d,t,l,z,c,s) ㄜ(e)
ㄎ、ㄓ、ㄔ、ㄕ、ㄖ(k,zh,ch,sh,r) ㄨㄛ(uo)
ㄅ?，?，?，?，?，?，ㄧㄝ。
ヵㄗ ㄒ(d, g, h, z, s) ㄟ(ei) is.
ㄈ(f) ㄚ、ㄛ(a,o)
ㄩㄝ(ue) boots, limping, ㄧ (when reading ㄐㄩㄝjue)
There are two ways to pronounce a word, the pronunciation is opening rhyme, the pronunciation is full of teeth and rhyme, and it must be entering tone.
If it is a nasal vowel (ㄢ, ㄣ, ㄤ, ㄥ(n,ng), it must not be an entering tone. (The exception in the first line of the above table is nasal rhyme. )
The initials,,,,) are generally not stressed (except "call").