Theory of Operation - Hardware

The Hardware

The hardware of Donkey Kong Jr. is very similar to Donkey Kong, but unlike DK the sound bit latches are all used ! An alternative is at hand because one of the features of Junior is an additional latch, which is used to control the second bank of graphics characters, with only two of the outputs of this part being used ! This leaves more than enough outputs available to control the serial EEPROM. Data output from the EEPROM is handled exactly the same way as with Kong and read in via an unused I/O lines.

Memory Control

The 74LS259 bit addressable latch at 4H controls all inputs into the serial EEPROM,

Schematics

EEPROM Clock, Data & Select

The Latch at location 4H on the Junior board only has 6 free outputs , Q2, Q3 and Q7 are used to control the serial memory.

Two control lines are required for Clock and Data Input and one control for Chip Select.

EEPROM Data Output

Just like Kong you can see from the schematics that there are a number of unused control input. So one of these is fed the serial data output from the EEPROM.

Note the 74LS240 inverts the incoming data !