Control Register 13

In 80 column text mode, this register is used to set the times of the periods of blinking of text colors. The text color defined by register 13 is displayed during the first period. The current color is displayed during the second period.

In graphic modes, this register is used to configure a cycle of two display periods of an even or odd page. The lower even page is displayed during the first period of the cycle. The odd page or the alternation of the two pages if bit E0 of register 9 is set, is displayed during the second period.

This register can be only written. Use the MSX-BASIC instruction VDP(14) to access it. The instruction reads the system variable REG14SAV (0FFECh) to return the requested value.

• ON0-ON3 bits set the time for the second period.

• OF0-OF3 bits set the time for the first period and enables the periodic display when any of these bits are set to 1.

Procedure in 80 column text mode:

1. Specify the text colors for the first period in the register 7.
2. Specify the text colors for the second period in the register 12.
3. Modify the color table in VRAM. This table occupies 240 bytes (0800h to 08EFh by default), each bit corresponds to character (24 lines × 80 columns = 1920 characters, hence 1920 bits, or 240 bytes). If the bit is at 1, the character flashes with the colors defined by registers 7 and 12, while if it is at 0, the character does not flash. It keeps the color of register 7.
4. Set register 13 with the correct display times.

Procedure in graphic mode (SCREEN 5 to 12):

Graphic pages come in pairs. In SCREEN 5 and 6, you can choose to display alternately pages 0 and 1 or 2 and 3 but never 0 and 3, 1 and 3 or 0 and 2.

1. Set bits N10 to N14 of register 2, in order to display an even page.
2. Set the respective display times and activate the periodic display using register 13.
3. Set bit E0 of register 9 to 1 to activate the alternation of 2 pages on the second period.

Control Register 18

This register can be only written. Use the MSX-BASIC instruction VDP(19) to access it. The instruction reads the system variable REG18SAV (0FFF1h) to return the requested value. It corresponds to the SET ADJUST instruction of MSX-BASIC, but without saving in the Real Time Clock (RTC).

• V0-V3 bits serve to adjust the screen vertical location. (0 at initialisation)
• H0-H3 bits serve to adjust the screen horizontal location. (0 at initialisation)

Please wait for the CE bit of status register 2 is reseted before accessing this register when the display of the screen or Sprites are deactivated otherwise VRAM corruption could occur.

Using this register to make screensplits can lead to uncommon results when the sprites are disabled. For example, the background color will be used for the current line by moving the screen to the left with control register 18.

Control Register 19

This register can be only written. Use the MSX-BASIC instruction VDP(20) to access it. The instruction reads the system variable REG19SAV (0FFF2h) to return the requested value.

• This register defines the line number where a programmed interrupt must happen when horizontal retrace interrupts are enabled (value 1 in bit 4 - IE1 - of control register 0).

The VDP will generate interrupt when it starts to display the scan line corresponding to the value written in control register 19. It will also set to 1 bit 0 - FH - of status register 1.

Control Register 23

This register can be only written. Use the MSX-BASIC instruction VDP(24) to access it. The instruction reads the system variable REG23SAV (0FFF6h) to return the requested value.

• D0-D7 bits defines the horizontal line number at which the foreground display begins. (0 at initialization)

Foreground height is 256 lines (0 to 255), visible part can be 192 or 212 lines depending of bit 7 - LN - of control register 9. At initialization, value of this register is 0 and lines 0 to 191 or 211 lines are displayed.

If you increase the value of this register, top of foreground will begin at the specified line. This register is used to easily make vertical scrolling.

Control Registers 26 and 27 (V9958 only)

These registers can be only written. Use the MSX-BASIC instruction VDP(27) or VDP(28) to access the corresponding register. The instruction reads the system variables REG26SAV (0FFFBh) or REG27SAV (0FFFCh) to return the requested value.

• HO0-HO8 bits defines the vertical line number at which the foreground display begins. HO8 bit is only useful if SP2 of register 25 is 1. In screen 6 and 7, the scrolling will be every two lines. (These two registers are initially reseted.)