sm rng routine commented

$80/8111 E2 20       SEP #$20	; set 8-bit mode accumulator
$80/8113 AD E5 05    LDA $05E5	; load low byte of last random number
$80/8116 8D 02 42    STA $4202
$80/8119 A9 05       LDA #$05	; multiply it by 5
$80/811B 8D 03 42    STA $4203
$80/811E EA          NOP
$80/811F C2 20       REP #$20	; set 16-bit mode accumulator
$80/8121 AD 16 42    LDA $4216	; load the resultant product
$80/8124 48          PHA	; push it onto the stack
$80/8125 E2 20       SEP #$20	; 8-bit
$80/8127 AD E6 05    LDA $05E6	; load high byte of last random number
$80/812A 8D 02 42    STA $4202
$80/812D A9 05       LDA #$05	; multiply by 5
$80/812F 8D 03 42    STA $4203
$80/8132 EB          XBA	; exchange high and low bytes of accumulator
$80/8133 EA          NOP
$80/8134 AD 16 42    LDA $4216	; load low byte of product
$80/8137 38          SEC
$80/8138 63 02       ADC $02,s	; add to it the high byte of the original product
$80/813A 83 02       STA $02,s	; save it to the high byte of the original product
$80/813C C2 20       REP #$20	; 16-bit
$80/813E 68          PLA	; pull it from the stack
$80/813F 69 11 00    ADC #$0011	; add 11
$80/8142 8D E5 05    STA $05E5	; save as new random number
$80/8145 6B          RTL