am79c30a Advanced Micro Devices, am79c30a Datasheet - Page 57

• Manufacturer Part Number: am79c30a
• Description: Digital Subscriber Controller ?dsc ?circuit
• Manufacturer: Advanced Micro Devices

IOM-2 Activation/Deactivation
The IOM-2 Interface includes an activation/deactivation
capability (see Figure 13). Activation and deactivation
can be initiated from either upstream or downstream
components on the bus. When deactivated, the up-
stream device holds all the clock outputs Low, and the
downstream devices force their open drain data out-
puts to a High-Z state (seen as a High on the system
bus due to the external pullup resistor). The activa-
tion/deactivation procedure is a combination of soft-
ware handshakes via the C/I channel, and hardware
indications via the clock and data lines. The IOM-2
specification describes both the hardware and software
protocols in detail; the hardware operation supported
by the Am79C30A IOM-2 implementation is outlined in
Figure 13.
Notes:
This diagram shows only the portions of the IOM-2 activation/deactivation procedures that are affected by the Am79C30A
hardware. The C/I-channel software handshakes are not shown.
Timing Request Interrupt generated
Software sets Activation bit
Software sets Activation bit
SBIN goes Low
SBIN output forced Low
clk pend
(clks off)
Software sets
(SBIN = 0)
(SBIN = 0)
Activation bit
(clks off)
(clks on)
Clock received from
upstream; Timing Request
interrupt generated
Figure 13. IOM-2 Activation/Deactivation
a. Am79C30A as Downstream Device
Am79C30A/32A Data Sheet
Software clears
a. Am79C30A as Upstream Device
Activation bit
(SBIN = data)
(SBIN = Z)
(clks off)
(clks on)
ACTIVE
(clks on)
ACTIVE
(clks off)
Idle
Idle
DSC/IDC Circuit as Upstream Device (Clock Master)
Deactivation
D e a c t iva t io n o f t h e IO M -2 I n t e r fa c e f ro m th e
Am79C30A operating as an upstream device is initi-
ated and controlled by the microprocessor. A series of
software handshakes via the C/I channel must be per-
formed before the hardware deactivation can take
place. The upstream device must issue a deactivation
request command on the C/I channel and wait for a de-
activation indication from all downstream units. Once
this is received, a deactivation confirmation command
must be sent on the C/I channel by the upstream de-
vice. The upstream device will then stop all clocks and
hold them Low. On the Am79C30A, the IOM-2 clocks
(SCLK,SFS, and BCL/CH2STRB) are stopped and
forced Low when the microprocessor clears the activa-
tion/deactivation bit in the Peripheral Port Control
Software sets
Activation bit
Clocks stopped by upstream device
SBIN output forced to Z
(clks off)
Timeout
09893H-9
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