Return to previous page ｜ Return to menu ｜ Go to next page

2.5 External signal and scanning status

The external signal enable register is used to control external signals, and the screen status register, H counter register, and V counter register are used to display the TV scanning status.

External signal enable register

External signal enable register controls signals from outside VDP2. This is a 16-bit readable / writable register at address 180002H. The value is cleared to 0 after power-on or reset, so be sure to set it.

External latch enable bit : External latch enable bit (EXLTEN), bit 9

Specify the condition for latching the HV counter value in the HV counter register. 

 EXLTEN 
 Articles 
 0 
 Latch when external signal enable register is read 
 1 
 Latch by external signal

∙ The latched H counter value can be read with the H counter register, and the V counter value can be read with the V counter register.
Set to 1 when reading H and V counter values ​​with an external signal such as a light gun. Normally set to 0.

External synchronization enable bit : EXSYNC enable bit (EXSYEN), bit 8
Controls the input of the external sync signal to the internal sync circuit. 

 EXSYEN 
 Processing 
 0 
 Do not input external sync signal 
 1 
 Input an external sync signal to synchronize the TV screen display with the outside

⿟ Enter 1 to synchronize screen display with other devices. Normally set to 0.

Image display area select bit : Display area select bit (DASEL), bit 1
Specify the image display area. Valid only when the EXBGEN bit is 1.

Return to previous page ｜ Return to menu ｜ Go to next page