MA28140 Datasheet, PDF (28/72 Pages) Dynex Semiconductor – Packet Telecommand Decoder

MA28140
In addition, the MAP interface provides the output signal
MAPSTN, in order to save the MAP identifier present on the
local data bus (LDAT<7..0>) in an external latch. This MAP
identifier is used to demultiplex the segment data toward the
selected application. The MAPSTN signal can be controlled by
the LACK signal. MAPDSR has no effect when MAPDTR
output is deasserted.
The output frequency for each MAP is programmable and
is defined in ROM. For MAP number n, the address of the
value X defining the MAP frequency is (hex) 100+n. The MAP
output frequency is given by F=f_ck/[2^X], (X is coded on the 4
LSBs and its value varies from 1 to 13; for other values, the
output frequency is F = f_ck/2). For example for a PTD clock
frequency of 4 MHz, setting the ROM value to 4 will generate a
MAP frequency of 250 kHz. With a system clock frequency fck
of 4 MHz, the MAPCK frequency can vary from 488 Hz (X=13)
to 2 MHz (X=1). The use of a too low MAP frequency
compared to the TC clock frequency may lead to the activation
of the WAIT flag if the MAP output of a previous frame is not
finished when a new segment arrives. As a rule of thumb, in
order to avoid the Wait flag being asserted, the MAP frequency
should be at least the TC input bit rate multiplied by 10 when
fully variable segment size (by 2 if fixed length).
Figure 11 describes the serial interface in three different
transfer situations.
Serial MAP Interface
PTD
PAR = 0
MAPDSR
MAPDTR
MAPCK
MAPDATA
MAPADT
APPLICATION
N maximum value is 1991 corresponding to a
TC segment of 249 octets.
Note: The bit 0 is the MSB and shall be transmitted first.
Figure 11: Serial MAP Interface
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