ZBasicSysLib - page 65 of 361

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ZBasic System Library

ZBasic Microcontrollers

BusWrite(addr, data, count)

BusWrite(addr, data, count, delta)

The bus address at which to begin writing.

The data to be written.

The number of bytes to write.

The amount by which the address should be changed after

each byte is written.

For ZBasic devices that support external RAM (e.g. ZX-1281), if the external RAM interface is enabled

and bus has not been defined using DefineBus(), then the external RAM interface is used for the write

operation. In this case, the full 16 bits of the specified address are used and the delta parameter is

interpreted as a signed 8-bit value that is sign-extended before adding it to the address with each

For ZBasic devices that do not support external RAM or if the external RAM interface is not enabled, this

routine performs a series of write operations on the bus previously defined with the DefineBus() call. This

is called the “bit bang” mode. For each write cycle, the low 8-bits of the address is output on the

previously specified port and then the ALE pin is strobed (high, then back low). Then, the next data value

to be written is output on the port and the WR pin is strobed (low then back high). Finally, the specified

delta is added to the bus address and the cycle is repeated until the specified number of bytes has been

It is important to remember that in the bit bang mode only 8 bits of the address are used. Depending on

the values of the addr, count and delta parameters, the effective address may wrap around to zero.

For example, with delta=1 specifying a count parameter larger than (256 – LoByte(addr)) will

result in the effective address wrapping around to zero.

In either mode, if the optional delta parameter is not specified, the value of 1 is assumed. Specifying

the delta as zero will result in multiple writes to the same address. A delta of –¹ or &Hff will result in the

address being decremented after each write.

Dim data(1 to 20) as Byte

Call DefineBus(Port.A, C.0, C.1, C.2)

Call BusWrite(0, data, SizeOf(data))

This subroutine is not available on ZX models that are based on the ATmega32 processor (e.g. the ZX-

24) nor is is available on ATxmega-based ZBasic devices. Moreover, it is not available in BasicX

compatibility mode.

BusRead, DefineBus