It is good programming practice to use the operating system calls provided rather than trying to manipulate the hardware directly. This avoids compatibility problems with future releases, and leaving the operating system in an unstable state. We are therefore NOT going to encourage the reader to poke to the screen or disable the operating system! However we will attempt to give as full a description of the hardware that exists as we understand it.
Overview of the BLINK registers
The following table lists all the registers in the BLINK chip, which are accessed through the Z80 I/O ports. Not all of the registers are useful to programmers, but they are all included for completeness. Some are described in more detail later in this section.
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The hardware registers have only one function. They can either be written to, or read from, (but not both). With this constraint it would be possible to lose track of register contents. To get around this problem, he the operating system use addresses $0400 to $04FF to store 'soft copies' of the values in the BLINK registers, with the low byte of the address being taken from the address of the I/O port. These soft copies can always be read, to check out the contents of the hardware registers. |
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I/O port WRITE READ
$70 PB0, pixel base reg.0 -
$71 PB1, pixel base reg.1 -
$72 PB2, pixel base reg.2 -
$73 PB3, pixel base reg.3 -
$74 SBR, screen base reg. -
$B0 COM, command register -
$B1 INT, mask & control STA, interrupt status
$B2 - KBD, keyboard
$B3 EPR, EPROM programming -
$B4 TACK, RTC ack. -
$B5 TMK, RTC int. mask TSTA, RTC int. status
$B6 ACK, main int. mask -
$D0 SR0, segment reg. 0 TIM0, RTC 5ms counter
$D1 SR1, segment reg. 1 TIM1, RTC seconds counter (6 bits)
$D2 SR2, segment reg. 2 TIM2, RTC minutes counter
$D3 SR3, segment reg. 3 TIM3, RTC minutes/256 counter
$D4 - TIM4, RTC minutes/64K counter (5 bits)
$E0 - RXD, UART receive data register
$E1 - RXE, extended receiver data
$E2 RXC, receiver control -
$E3 TXD, transmit data -
$E4 TXC, transmit control -
$E5 UMK, UART int. mask UIT, UART int. status
$E6 UAK, UART int. mask -
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