saa5355 NXP Semiconductors, saa5355 Datasheet - Page 23

• Manufacturer Part Number: saa5355
• Description: Single-chip Colour Crt Controller Ftfrom
• Manufacturer: NXP Semiconductors

Philips Semiconductors
The display memory organization uses the word/byte addressing convention adopted for the SCN68000 microprocessor
series. Data fetched on the 16-bit bus is considered in terms of bytes where the even numbered bytes use the upper
(most-significant) part of the bus as shown in Fig.19. The word addresses are numerically the same as the upper byte
that they contain - there are no odd-numbered word addresses.
Warning time
As FTFROM is a real-time display device, it must have direct access to the display memory with priority over the
microprocessor and other peripheral devices. This is achieved by FTFROM issuing a bus request (BR) signal for the
duration of the memory access plus a programmable advance warning time which allows the microprocessor to complete
its current bus cycle.
In systems where the buses of the microprocessor and FTFROM are intimately connected (connected systems), BR may
be used to suspend all microprocessor activity so that FTFROM can act as a dedicated DMA controller. In systems where
the two buses are separated by buffers (disconnected systems), BR may be used either to generate an interrupt or as a
direct signal. To these ends, the warning time between the assertion of BR and the beginning of FTFROM’s bus activity
is programmable to be between 0 and 22,84 s.
March 1986
Single-chip colour CRT controller
(FTFROM)
Fig.19 Display memory word/byte organization.
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Product specification
SAA5355